From the games you listed..
Ut2004: they have a native Linux version. They even include the linux installer on the cdroms. Check out
http://icculus.org/lgfaq/gamelist.php for details and updates.
http://icculus.org/
HL2/Steam/CS:Source: no chance in hell for a free version. That game has so much DRM crap it'll make your head spin.
That's one of the reasons why you have to use Cedega for games. When they incorporate protections into installers and stuff like that Cedega is able to license the technology to get it to work in Linux. Actually many windows-only game makers and anti-piracy stuff will actually work with Cedega to make sure that their stuff will work in Linux. But aside from Cedega's Directx 9 implimentation the major thing is licensing restrictions with the games you want to run.
Many games that will run on straight wine or the free versions of cedega code you can get require that you install them first on Windows then copy the game content over....
World of Warcraft will work on CVS versions of Wine with Wine's Free Directx9 support... But you have to know what your doing.
The 5 dollar subscription fee is minimally 3 months, if all your games work you can simple cancel it and you can still continue playing those games. It won't shut off on you.
For more information on wine:
http://appdb.winehq.org/
For more infromation on wine apps howtos:
http://frankscorner.org/
Should realy check out free software games, though. Some are very nice and almost all are designed to run on older hardware. A good example is Vegastrike, which is a wingcommander-style game and under constant developement. It's requirements are something like a 600mhz Pentium3, 386 megs of RAM, and a 16 meg video card and it's actually nice looking. If your using Debian or Ubuntu you can install it just by going apt-get install vegastrike, if you have the source.list setup with the extra repositories and such.