The beta demo is free to download anywhere , no key needed
i think you can run it on your computer ,
you can adjust , texture size , detail geometry etc ..
if you have standard shaders: normal/specular that any old Piw shader V2 or perhaps older (1.4) can run , it should run.

Lot less beautifull , but it should run

Just watch some screen capture over the net of the demo , to see what you can have on a good pc.

For my part , even if i find it less more eye and colours catching ,
i will prefer to play Call of Duty 4 (and it's great multiplayer mode)