I have been running FS2K for nearly a year now, and apart from a HDD problem, not to do with the sim, I have found it perfectly OK.
I have a seperate drive with 6.3gb to run both FS98 and FS2k, there are add-ons that are compatabile and work with each other. I have a Celeron 533, 128mb of RAM, and a G400 Matrox card. Everything works well, but I recently watched a GE Force256 at work and have ordered one. My frame rates on FS98 are 90+ and on FS2k in excess of 35, which is fine. But I want better 3D, GEForce will provide that.
I must say I am curious about the amount of space take up on Bokk's machine, shouldn't be that high. I suggest that you kill it and start over. I have 5.2gb spare with both sims on my hard drive so something is wrong, and that includes quite a few add-ons and panels etc.,