Browsing around instead of working, I came across this little gem:
http://www.gamespot.com/features/6147127/index.html
Apparently the actual Obliv forums have a lot more in-depth performance ideas (many including actually going into game files and modding bits and bobs to get better FPS rates), but this is enough to get me going without having to devote a huge chunk of time to it.
Any other peeps who have the PC version might consider checking the article out. I found it very interesting, and nothing too technical for the less-tech savvy amongst us...
Now where's my fiancee's old system... must scrounge RAM chips...
Kev