Call of Duty 2 doesn't work on Linux (via Cedega, the Windows game wrapper). Guild Wars, on the other hand works. I suggest using SuSE Linux since I find it's the perfect combination of ease of use and power.
NOTE: Cedega does cost some $$$. $5/month subscription required (min. 3 months).
Here's a list of games that do work on Cedega: http://transgaming.org/gamesdb/
Specs: AsusTek P4B533-VM, Intel Pentium 4 2533MHz, 120 GB HDD Maxtor, 80 GB HDD WD, 1GB PC3200 RAM, NVIDIA GeForce 6600, openSUSE 10.2 (Main), MacOS X 10.4.5 (leisure use, backup)