explorer.exe is constantly at high CPU? I'm on WinXP Home, 512 MB ram, and 1.8 GHz.

When I browse Windows Explorer, or do many other actions, explorer.exe
constantly shoots up to 100% CPU usage. My C: drive is 54 % data
fragmented, and 1% overall fragmented. Could this be causing it?

yes... explorer is the windows shell that you use to interact with the
OS.  It is what houses the windows menu and the clock etc.  You should
definately defrag the HD to improve seek times and cut down the amount
of timeit takes your computer to find the data it needs.  Furthermore
you should probably remove programs you dont need and use MSCONFIG
(start it from the RUN menu) to disable unnneccesary programs from
starting up when you turn on yourcomputer.

It is ofcourse possible that you have some malware running. 
Personally I would recommend going to:

http://www.experts-exchange.com

This really is one of the best sites around for such a problem.  They
might recommend that you run:

http://www.webattack.com/download/dlhijackthis.shtml

and put the log file into your question.

BB

I've run tons of scans on my PC and it has found nothing wrong. I have
been using this PC for 2 years, about 6 months ago CPU usage has been
shooting up

There more than likely is spyware/virus or a combination of both at
work on your computer.  I have had this trouble brought to my
attention several times from friends and customers, in fact, I have
had the same trouble on my own computer.  First, how well do you
understand your computer.  This will help me in determining the
easiest way of helping you.  One thing you will want to do is run
ADAWARE, SPYBOT, AVG Virus and ANTIVIR before doing anything else. 
This will ensure that most problems will have been taken care of. 
Most times I find that a virus or adware/spyware program has taken
control of the peoples LIMEWIRE or KAZAA program which in turn drives
EXPLORER crazy.  Go to your ADD/REMOVE programs and make sure you have
all the spyware removed (gain, ebates, etc.) and remove either of
those programs if you use them.  Reboot your computer and reinstall
the programs if EXPLORER has calmed down.  I Hope this helps.  If you
need more details, you may contact me.

Troubleforu - www.defiantprogrammers.com

Have you got a scanner installed - in particular an HP Scanner. If so,
try to disable it in Device Manager and see if it makes a difference.

I had a computer that was having the same exact problem. I used
Hijack-This to remove the spyware culprit. Other spyware removal tools
would not work.

i also have the problem of a over active CPU,
but you guys tell my it's hijacking ... but i pulled out my internet cable.
i also did a scan with the hijakcthis program,
the only problem is that i dont know what i can delete and what not...

plz help