How would I go about adding another hd to my pc for fs only and have all other programs and os on the main drive? What is their to look for besides space when picking a hd? Would I just copy the ms games folder to the new hd and leave it at that or would a re-install be required?

I would completely reinstall just to be on the safeside. I too have a hard drive dedicated to FS9, and my 80 gigs is filling up fast (when you constantly install addons and modifications), etc.I got a USB plug in one, so I can move it around if needed...That's one thing I would consider other than space.