If your intent is to create a level for MWLL, you should be using either Vista or Win 7 64 bit. The 32 bit operating systems do not cut it for creating the large maps used by MWLL. Also you should have at least 4 GB of main memory and it would be nice if you had at least 1 GB of GPU memory.
Actualy my 32 bit xp rig is what i use with a slightly OCed amd dual core (gotta double check if its athalon). I got 4 gigs of g skill ram at 1066 on a gigabyte board( im cuting out a gig here due to 32 bit im aware).Also im runing only the onboard ati 4200 hd...yes i know i need a 64 bit sys and all that to realy apreciate crysis but for now it works. I intend after geting a new car to go ahead and get a new mobo cpu and video card giveing my old one to my gf.
EDIT: got home ran cpu-z just to double check everything and heres what i got.
athalon II x2 240 OCed to 3.1 ghz
2x2 gig g skill chips dual channel 5 5 5 15
ati radeon hd 4200 700mb mem
also when i first got this rig and was OCingi did several stability tests only a few failing once i got my currentsettings setup before that i failed a bunch took a bit of tweaking but there ya go