Obviously that makes me think it's something in my system.
I do not want to belittle your problem : just give you some feedback.
I run SINS on Windows XP 32-bit, also with a GeForce 6800 (December 2007 drivers : 169.21), but I only have 1GB of RAM.
What you describe never happened to me (and I have been playing this game since the June 2007 beta version). My hard disk has never been accessed with any annoying frequency. The game runs very smooth, with no stalls and stuttering.
What I do to minimize potential problems is :
1. Close all user-defined background programs (such as an antivirus) before launching the game (only the necessary explorer.exe remains). This reduces possible causes of interference.
2. I installed the game on a secondary hard disk (not on the primary C:\). I do not know if that helped. (I defrag both disks at least once a week.)
3. I play the game in a 1360 x 768 window (on a 1440 x 900) desktop, with all the graphical texture-quality settings defined at "highest", but I disabled a few minor features to unburden my system (the planet "elevators", the tiny asteroids, etc.). My 6800 handles the graphical workload very well.
4. But I have only tried maps with one star, 15 to 30 planets, 4 players. I do not know if 1GB of RAM and a 2½-year old 6800 model will cut it in a bigger "galaxy".
5. I run 3 different anti-spyware/malware programs regularly. If you have a "polluted" system, your hard drive will of course display weird activity, at times.
Good luck in fixing your problem : with 2GB of RAM and a 6800 GT, you should be able to run that very beautiful game smoothly.
