How to make a mod to massively improve performance?

[forhotc]

Hi there, I'm just wondering is it possible to make a mod to massively increase the game performance (in terms of frames per second)?

My video card is fairly old, Nvidia 7600GS, and only the lowest graphics settings are actually playable. However, I always have this strange habit of tweaking the deck guns to fire at crazy rates (like 10 shots per second), but thanks for the poor video card, the actual firing rate is always a lot lower than that (like 2 or 3 shots per second), because it just can't display that fast. (CPU and RAM might not be so much of a limiting factor here: P4 3.0G and 4GB RAM)

So, could you guys provide some direction about: the aspects of the game that I can tune down that actually effect performance; ways of tuning them down, such as editing via S3D, changing values in some configuration files, removing under water rock/plant files, etc; If I need to use lower res texture, where I can find them or how do I make them...

I know the best possible "mod" is actually "buying a new video card", but Aussie dollar is so low at the moment and I'm going to wait until mid year to get the whole Intel i7 and video card upgrade.

Thanks a lot in advance.