I have a Q9450, 4 Gigs RAM and 2x 260 Nvidia GTX's SLI'd running @ 1920x1080
Better than my rig by a long shot. While I don't get phenomenal framerates, I'm comfortably playable on an older card (a slightly-overclocked GTS 250 that nets me about 30 fps in combat, give or take a bit depending on the map)
If you have framerate trouble, disable SLI and run on only one card. I've been told CryEngine 2 has...
issues with SLI, to the tune of doubling or tripling framerates
without it at times, though that may have been a problem with Vista not liking GeForce drivers, as I'm told Cossfire setups had better luck. Mind you, my information dates to around the release of Crysis, so things may have changed since then.
In any case, Warhead/Wars is $20 on Steam and you might be able to find it cheaper if you're willing to brave a GameStop (or similar). Warhead is actually a fairly amusing game in itself, and while I would have regretted the price for it alone, it's a steal considering I'd be perfectly willing to pay full new-game price for MWLL.
Well, your processor is the weakest link, but I'm sure overall you'll be fine.
Q6600 here. So long as I turn off some of my background stuff, I'm fine.
Speaking of which, it's also worth pointing out that once Wars/Warhead is installed and run once, if you go with the Steam version, you
don't actually have to be signed in to Steam in order to play MWLL.