I wrote in a forum recently that I suspected some timing issue somewhere, and that FSUIPC was either getting bombed out by the window switch or was letting go of the sim in some way. Primarily because although the PC was way fast enough for the sim, I observed that fs2002 window switch was much quicker than as for 2004. Thus, there is something about 2004 timings which is diferent than it's predecessor.
Ok here's what I did: In XP, uncheck window animation:-). Use XP style desktop, not windows classic (possibly something is running ) Now minimise and restore a few windows, any will do and you might well see a noticeable inrease in speed when they switch. This suggests window animation may be upto some mischief.
Now start the sim and get into flight window, full screen view and then minimise, but DO NOT minimise with alt+enter or mouse. Instead from the full screen view minimise using the 'windows' key ONLY, located at lower left hand of keyboard. Restore at your liesure with l/h mouse click on task bar sim indicator. This will not crash or hang the sim and affords quicker access to other windows anyway. Note also abcense of 'beep' when using this method, why? i wonder.
By this method I swear I must have toggled windows in 2004 about 100 times, not one single freeze.
Perhaps this may shed light or give some hint as to what is going on, I would hedge a bet on FSUIPC not being quite at home with timings, somewhere.
Merlins