I can run Oblivion with my 5200 (check sig for more details) but at horrible quality. I mean horrible. It's only playable if you run it with a special texture mod. Also, the 5200 doesn't support SM2, and Oblivion runs in SM2/3. Gothic 3 will almost certainly be SM3; the point is that you will be able to play IF:
You optimize your PC - kill any processes taking up RAM and CPU cycles (*cough* Norton), as Oblivion uses all of the cycles, almost constantly; and when I've played for longer than 30 minutes or so, Oblivion manages to rack up 800 megabytes of RAM.
Optimize Oblivion - this is a long, involved process which requires lots of trial and error - mainly editing the Oblivion.ini file.
Gothic 3 is most likely out of the question, as it's graphics are a few months more advanced than Oblivion. If you want to play Oblivion at an acceptable (20+fps outside) rate and with eye candy (and no occasional artifacts), I would say it's probably up for grabs, 50-50, since I don't know how good a 7400 is.
If you decide you want to give Oblivion a try, you can PM me and I'll e-mail you my tweaked Oblivion.ini