Well, I've just had the best 2 hours of offline flight simming I can remember...

[SEE]

XP is listed on the system specs and on the DVD case, to me that confirms it is supported.

I did not have any rendering problems even though my GTS250 only had 512Mb of memory, most that did were using ATI cards.

I read your post and what struck me was that there were no problems prior to some of the updates. You should be running with DX9 if using XP so might be worth checking that your cnfg file has not been changed to DX10.