I have the comp in my sig
I run the games that support widescreen at least mostly at 1680x1050 it does a pretty good job my computer is also worse than yours by a little 3200+, 1GB.
I play oblivion at 1680x1050 grass turned off with playable frames it gets slow in certain areas mostly fire and alot of people fighting.
to give you an idea of the games I can play fine:
cs 1.6 @ 1680x1050
cs:s @ 1680x1050 i turn off AA/AF for higher frames but it's not bad with some AA/AF
HL2 @ 1680x1050 I play with some AA/AF with cs:s I recommend turning off though
HL2 EP1 @ no AA/AF I recommend
BF2 Demo @ 1680x1050 with widescreen fix not true widescreen but good frames
Tiger Woods 07 @ 1680x1050 fix gets low frames in certain areas but very playable
NFL07 @ 1280x1024 doesn't support widescreen plays great
SWAT 4 @ 1680x1050 fix plays good
NFMW @ 1280x1024 doesn't support widescreen plays great
Far Cry @ 1680x1050 plays good
Doom 3 @ 1680x1050 fix seems to play good I thought Quake 4 and Doom 3 were based on same engine though.... maybe true Doom 3 is mostly indoors not as much as Quake 4.
Quake 4 @ 1680x1050 ****** engine plays like ******
The Regiment @ 1680x1050 plays good
My new comp will play em better though

E6600, X1900XT, 2GB
Edit: Left big space at bottom idk how