I have two computers that I would like to sell or donate but before
doing so I want to be sure that none of my personal information is
still on the machines.  1) How do I go about erasing all personal
data?
2) If I sell how do I determine a fair price? 
one machine is a Sony Vaio and one is a Mac (G3 I think)- both
purchased around 1998.

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Clarification of Question by ledman-ga on 18 Nov 2005 11:48 PST

I do not want to have to purchase a program in order to erase the data
- is there a way I can do it myself or do any retail outlets provide
the service?

Please take look on following program:
http://www.acronis.com/enterprise/products/drivecleanser/
It will do what you need for your PC. 
For mac, you can connect Mac's drive to your PC and use same program.

regarding prices, I would say look on eBay and see what is middle
price for same or almost same units. for example, if on eBay you will
find G3 system with 1gb of memory, but yours has only 256mb of memory,
you can deduct from that auction price like $20-$25

I'm not a researcher but would like to be.

For free secure data removal tool see 

http://sourceforge.net/projects/eraser

1.  This is a boot disk that will wipe the data from all drives in the
machine.  It's appropriately named, boot and nuke.  There a version
for both mac and pc:

http://dban.sourceforge.net/

2.  The computers are 7 years old.  I wouldn't even bother to sell
them, but would instead donate them.  If you are intent on selling
them, I'd price them at around $50 - $100.  You can get an idea what
like computers sell for by checking completed auctions out on eBay.

1) Why not format it?  Free, fast OR Buy a new hard drive, a brand new
clean no nothing hard drive!

2) How much did you buy them for?  Add the money for the hard drive
and 1 extra dollar!

hii my friend, 
you cab format ur harddisk and erase all data from ut . 
i have no idea about the prices but you can surf through net to find a
suitable one . thanks .

barkybb:

1.  Formatting is not very secure.  If you do a simple format, a lot
of the data will still be recoverable.  Buying a new drive isn't a bad
idea, but it's not very practical either.

I'll assume you have OSX on the Mac. The way I did the same thing on
my powerbook was through the admin account. Click on system
preferences and choose accounts. Create a temporary administrator
account with an easy username and password. Then log out of your user
account and relogin under the temporary user. Once logged in simply
trash your user account home folder. This should take care of your
personal info, just trash (or secure empty trash) any other programs
and stuff. Then be sure to give the tempporay admin user inforamtion
to the eventual buyer of your computer. I'm not well versed with
Windows but I bet a similar approach might work with it as well

YOU WANT TO SELL A 7 YEAR OLD COMPUTER?!?!?
You gotta be kidding right?  Here is a legitimate price, $20.  Just
give it away or trash it, nobody will even look at it for over $50.  I
cant believe feldersoft said $50-$100.

Use these free tools available from the Sourceforge site:
(I got the links from comments above ;)
Boot and Nuke - http://dban.sourceforge.net/
Eraser - http://sourceforge.net/projects/eraser

Reformatting does not erase the whole disk,  only the beggining of the
drive where all the pointers are to the rest of the data.  A sneaky
resourcefull person could scan the drive and collect whatever data may
be on the rest of the drive.  The eraser programs above will write
random 0's or 1's to the ENTIRE drive, killing off any usable data. 
However, if you are a secret spy,  the CIA and NSA have hardware
capable of reading latent electromagnetic singles off of drives that
have been overwritten by other data.  In which case the only secure
solution I would say is,.....  a handgrenade.

latent - 
Present or potential but not evident or active: latent talent. 
Pathology. 
In a dormant or hidden stage: a latent infection.

"YOU WANT TO SELL A 7 YEAR OLD COMPUTER?!?!?
You gotta be kidding right?  Here is a legitimate price, $20.  Just
give it away or trash it, nobody will even look at it for over $50.  I
cant believe feldersoft said $50-$100."

Did you even check eBay before posting?  For whatever reason, Macs
hold their value.

Here's one that needs parts that's going for $41:
http://cgi.ebay.com/APPLE-Power-Mac-G3-Tower-400Mhz-NEEDS-PARTS-TESTED_W0QQitemZ5833395907QQcategoryZ14911QQrdZ1QQcmdZViewItem

And another going for $119
http://cgi.ebay.com/Apple-Blue-and-White-Power-Mac-G3-LIQUIDATION-SALE_W0QQitemZ5834597276QQcategoryZ14911QQrdZ1QQcmdZViewItem

I can't believe you'd doubt my claim before checking the source that I
gave for backing it up.

do you have mobile disk,replace the harddisk you wamt to sell in the
mobile disk box,and connect to the another for format it.

IF you have OS X on the Mac you can use the disk utility. Select Erase
Disk and tell it to do its 3 time write over. That should work fine.
If you aren't using OS X then you will probably have to look into a
3rd party solution.

dont buy new hard disk might cost you more than your old computer,just
format and reinstall the operating system,that should be fine,if you
are still worried about data being compromised only thing could be
just to trash the system physically as proper software to erase all
tracks could be more expensive that intended cost of computer
thanks

First of all, if u want 2 erase all the data then boot ur pc with CD
ROM and format all the drives. This is the best way to delete!

Secondly, i think its difficult to predict the price because there are
lot of brands now with different prizes. I think you can estimate it
1/3 of the original price!!

Not for nothing, but I've been doing computer security for a very long time.

If it ever possibly contained any confidential data I recommend
drilling a hole through the hard drive before discarding it. A number
of businesses follow that rule. A large hammer works well also.

It is possible to recover data which has actually been overwritten
multiple times (not just deleted or the drive reformatted.)

But for all practical purposes you are probably safe enough just using
a multiple file wipe program unless there is something really bad on
that drive.

Practically speaking, 7 year old computers aren't worth anything to
most people unless guaranteed, reconditioned, or have parts someone
needs, they have passed their useful life and components are going to
start failing pretty quickly - laptop screens in particular have a
very limited life.

Personally, if I were to sell them on eBay I would simply pull the
hard drives and sell them without, a buyer for this technology likely
has one or needs parts.

Of course if you don't already have an eBay account and a good rating
people will be pretty leary of something like this - donation is your
best bet.

Good luck.