Low Frame Rates

When I run R4, some scenes play pretty smoothly, but others run at low frame-rates (>30fps), and I noticed that my CPU utilization is only around 30-50% I was wondering what factors affect the frame rate?
My CPU is 2.4Ghz Pentium 4
I have 1024GB RAM
and my video card is a GeForce FX 5600 (w/256MB RAM)
When I first got R4 a few years ago, it ran realy well, but recently it's been running slower than it used to.
My CPU is 2.4Ghz Pentium 4
I have 1024GB RAM
and my video card is a GeForce FX 5600 (w/256MB RAM)
When I first got R4 a few years ago, it ran realy well, but recently it's been running slower than it used to.