Call of Duty 2 is a task on some PCs. I turn down the settings pretty low on mine and I'm only running a Pentium 3, 512 of Ram, and an Nvidia 5200 card. If I get on a server with low ping on the multiplayer game, I do ok, but if I'm playing the game on single player... even with settings and anti-aliasing turned down/off I lag like crazy.
Call of Duty United Offensive is the sequel/expansion pack to the first game and both COD1 and COD UO can be bought as a package deal for fairly cheap but you need COD1 to play UO. To me, gameplay on United Offensive is better than any WW2 game I've ever played. Graphics might not be as sharp as COD2, but driving various vehicles in multiplayer, the ability to sprint, etc. all makes UO a better game. Plus almost any PC can run the first games.
The COD franchise is dead for PC and is now going to be released on console systems only. COD 2 was and will be the last PC game for the series.