Would Call of Duty MW2 be playable with a ATI HD4350 512MB, Athlon 64 3000+ and 1GB of RAM? If yes what kind of graphic quality level can I expect @
1280x1024?
Very low, the 4350 is not really a gaming card, it is better suited to HD playback and 'normal' tasks.
Consider dropping a HD4650 in as a replacement, anything more will be severely restricted by the 'slow' CPU.