Well you could always OC the 3000 to the 3200, but there isnt too much of a performance difference esp. if you are mainly using this comp for games. The things that really matter for games is your GPU and RAM. If you could I would suggest getting 2x 1GB modules since Oblivion could def. use that and 2 x 1GB modules you can easily get for around $135 (Monarch Computers and Newegg check out). I just suggest this since games will def. demand more than 1GB to play smoothly.
But no matter what I def. suggest you get a good PSU....The ones that comes with the cases suck and sometimes blows the whole system up. Look for a 450W PSU made by Thermaltake, OCZ, Antec (Take a look at the Antec SmartPowers, they are cheap and reliable).
Otherwise looks good.
RIG #1 - See System Specs.
AMD X2 3600+ (AM2), Biostar TF550, 2 x 1GB Buffalo Firestix, XFX 9800GTX+, WD 250 GB HD, NZXT Nemesis Elite Case, Lite-On Combo Drive and Lite-On DVD RW Drive, Antec TruePower 550W,
20.1" Dell w/ 17" Sony LCD