I've never even seen an FX 7300 at all. If you mean the GeForce 7300 then which one? The 7300GT is the most powerful of the lot and if you have that, you can expect to play Oblivion on mediumish settings pretty smoothly. There are other lesser versions like the 7300LE & the 7300GS. So make sure which one you have.
The GeForce FX Series is the 5th Generation of the GeForce family.
After that the simply started using numbers again like GeForce 7600 GT.
And to answer your question no. That card will not run good. I have an AMD Athlon 64 X2 3600+ Brisbane, 1GB of Corsair DDR2-667 memory, a Biostar tForce 550 Motherboard, an an eVGA e-GeForce 7900 GS 256MB, and I can't play Oblivion in high. I can play it very close to high but my system just can't pull it off.
I have the 256MB NVIDIA Geforce 7300LE TurboCache running on; AMD AthlonTM 64 X2 Dual-Core 3600+(1.9Ghz), 3GB Dual Channel DDR2 SDRAM at 800MHz- 2DIMMs, Sound Blaster Audigy Sound Card.
I mostly use Steam(Counter-Strike and Team Fortress Classic). I can actually Run Counter Strike in window, Anti Virus and Spy software, running, listening to my favorite music of my hard drive(Windows Media) and write this message.
Also I watch DVD's through this card into my Plain Jane T.V. and get a great picture. I like the card a lot. I'm pretty sure this card can run in parellel with another graphics card as well. My opinion on this card is, a lot of bang for your buck!