I only use the computer for flight sim so I see no reason to upgrade. Everything else works fine. There's no way to get an earlier version of the product so that I can continue using the product I paid for?
No, unless you have a backup of the old installer.
It's *because* you use the PC for flight sim, that you SHOULD upgrade! Unless your XP is the very seldom used 64 bit version (which would give you lots more problems since almost nobody writes drivers or supports it), assuming you use XP 32 bit, using it for Flight sim is VERY wrong.
The reason for this, is that a 32 bit OS can only "see" 4GB or RAM IN TOTAL. This includes the ram needed by Windows itself, the VRAM of the video card, and the RAM needed by FSX.
They will ALL share 4GB of RAM in total, regardless how much overall RAM you have in your system. So, if you have more than 4GB of RAM and you still use XP 32 bit, your extra RAM is completely wasted.
And, having Windows + FSX + video card VRAM to share 4GB in total, is asking for trouble, since FSX can easily take more than 3GB by *itself*, with the recent complex planes and sceneries.
With a 64 bit OS (from Windows 7 onwards), at least FSX could use up to 4GB for itself without having to share it with everything else, so Windows could use other 4GB.
If you still insist using XP, you will have far worse problems that just not being able to use GSX.