I would like to download old computer game(real-time stategy) classics
like DUNE2, Warcraft...etc(preferably for free or at a cheap price).
Can you tell me the addressses for the sites for downloading old
computer games?(Please make sure the sites and/or links work)

You can search for "Abandonware" .. Home of the Underdogs is a
noteable source. However, Warcraft in particular is probably not
available for download from reputable sources, as I'm sure Blizzard
would have something to say about it. Abandonware is a very gray area
and may be subject to the GA Terms of Service regarding illegal
information. I want to make it clear that I am not attempting to
provide information for illegal activities. But, you may expect that
this question  may indeed be deleted for that reason.

A simple word of caution.  If the games are offered free or for a
small charge, read the fine print.  Nothing is free.  What may happen
is, as they give you the games free they will also download spyware.  
What spyware does is transfers info about the place you go on the
internet to adware companies.  And then you may start getting popups
etc.

I have an employee who loved to download screensavers - Free.  I was
using her computer one day, she was on vacation, and the computer was
running REALLY slow.  I downloaded a anti-spyware program (free, I
know what your thinkin' ). By the time it was done she had over 1000
spyware type programs on that computer.  I ran the same program on my
computer, which had NOT be checked in over a year, I had 40.  Which is
not bad.

Just for your info, the program I used was Adware.  

http://www.lavasoftusa.com/software/adaware/

This wikipedia entry has a list of "Abandonware" games (probably not
completely up todate) and there is also links to abandonware sites:
http://en.wikipedia.org/wiki/Abandonware