If you're running dual core processors try, this:
Do a Ctrl/Alt/Del to bring up the task manager,
Right click on the FS Process (FS2000.exe)
Go down to 'Set Affinity'
Uncheck one of the processors (doesn't matter which).
See if this helps. I don't know if Vista will let you set the compatibility like XP, but if you can, do this:
Right Click on the shortcut for FS2000
Click the 'Compatibility' Tab
Set the compatibility to FS98
I hope this helps...