CNC3 Performance Problems

Hi guys,
I play CNC3 (original, not expansion) on a 2.2 SR MBP (In Boot Camp in XP), and used to get pretty good performance at native res and everything on Ultra High (except FSAA, which is turned off). Now I've started playing it again after taking a big break from it, the performance is somewhat dismal. To get reasonable framerates now, I have to decrease the screen resolution to a pitiful 1024x640, with everything on Medium, and it still chokes up at some points. Clearly this is a huge difference in performance. The only differences that I can think of is a few extra programs I've installed, and the fact I'm running it off an external USB HDD.

Any ideas or things I can test to identify what the hell is going on would be much appreciated.
Thanks.

Have already been using laptopvideo2go drivers for a while, and updating them every now and again. Also tried using Apple's Leopard drivers. No good.

It seems this problem is not only CNC3, either. Oblivion is also slow, and I'm not even going to try Crysis.

How do I find out if my computer has downloaded SP3?

And I've been running Oblivon off the external forever. I don't think that's the problem.