"It really doesnt make sence for Halo not to run well on a top of the line Nvidia card since Halo on Xbox (which is a Gforce 3.5) ran just fine"
First off, the XBox only had to run the game in 640x480. And even then, I learned a few ways to make the game run really slow in certain parts.
Second, the XBox is a single platform that only has to do one thing: play games. It doesn't have to worry about too many background processes or discrenpencies between different XBoxes. The PC version has to run across the different OS's, and handle the different hardware configurations out there. This increases bloat and decreases performance.
Lastly, it wasn't simply a GF3-series card. Reading some of the FAQs and what-not, the development team said they had to COMPLETELY re-write the animation code, as that was code-specific to the XBox. I'm sure there were other parts where the code wasn't standard DX9 code, but specialized code.
"Space. It seems to go on and on forever. But then you get to the end and a gorilla starts throwing barrels at you."