I've also had this problem, except that the flashes happened much more frequently. Lunar Pilot, if it's not much of a hassle, open up a small window like the Ctrl-space one or the Orbiter menu with F4. Other windows seem to fix the problem.
Of course, I no longer have the problem, and I think it was because I partially reinstalled Orbiter (I copied the new download over my old one without removing any of the add-ons). The last thing I did to my system was unplug it and clean out it's insides with propane gas (unorthadox, I know). I would suggest reinstalling Orbiter first.
dxdiag gives near exact same specs for me except two main things.
For him it says, Monitor: Plug and Play Monitor . I'm not too sure what that means, and it doesn't sound right. For me it gives Monitor: DELL E177FFP (my monitor model obviously)
It just means it's one of the cheaper, more generic monitors that came with the setup from Dell. I've got one (PnP monitor) too. Did you buy (or upgrade during the purchace) a new monitor?
The other difference is that my computer only has 512MB RAM but that shouldn't affect anything.
Same here, it dosen't seem to be the problem though. I've also got the same graphics controller and drivers as him, but on a Dell Dimension 3000.