FPS is going hangwire

Suddenly my FPS for games has started going hangwire. Here's my specs;

Windows XP Pro SP2
Intel(R)
Pentium(R) 4 CPU 1.70GHz
1.69 GHz, 768MB of RAM

At first when I started using the thing, it ran just fine and would work even with a few programs running in the background. But now the FPS just drops down to 3.00 all the time. I'm using the default Jabo's Direct3D6 1.5 plugin for the video as well. Any ideas on how to fix this? So far I've noticed it slows down with all my few games (Only being Super Mario 64, Mario Kart 64 and Paper Mario).

Also, can I get some suggestions on what plugins would be best for my rig? Thanks in advance.

NVIDIA GeForce FX 5200

I'll also try those plugins out too.

Alright, I updated my driver but that didn't solve it either. I'm starting to think maybe it's not Project64, but the ROM's I am using. Because Mario 64 seems to run just fine, but every other rom I got from that site just runs like crap. So I'm going to try another rom from a different site (if I can find one) and see what happens then.