Ran pretty "well" on my system too...
AMD Athlon 64 3700+
2gig of DDR1 PC3200
ATi X850xt
SB Audigy 2 ZS
*When installing the demo, be sure to also install DirectX when it prompts you to as the game needs/comes with the latest DX9.0c build. The game wouldn't run for me the first time I chose not to install it.
My list of whiney complaints and praises...
-lack of a "select-fire" mode, there is no excuse for leaving this out from COD4 since 1 and 2 had this feature (perhaps I didn't find it?).
+They got the hectic and intense battlefield atmosphere down really well.
-HOLY CRAP, a Javalin shooting up, up, and away into the atmosphere!? What is this?! A fricken portable orbital missle? Yes, I know things like these were done for the sake of "fun" but come on, don't take this into the realm of extream fiction (nag).
...I can't help but feel as though COD4 will be sort of like a Battlefield 2 with a story single player mode. I probably won't be grabbing this right off the shelf when it hits but look forward to playing through the whole campaign a see what crazy ideas they come up with. The multiplayer looks extreamly fun as DM style game.
Really in terms of infantry combat, all I really ask for is a visual mod for Red Orchestra that switches out the WW2 stuff for modern weapons. I'd be a happy camper till the end of days if that ever happens.