I haven't followed this accurately so I apologise for any repetition. For WinXP there is a /3GB fix that is available. This allows FS to allocate more than the fixed 2gigs. It seems to be well established. There is also a 3GB enabler that can be downloaded from Game forums for Vista, which involves rebatching FSX.exe. If you look at the Flightsim forum there is plenty of reference to this. Phil Taylor warns against this because of a DSD bug in FSX - something I thought would have been corrected as his bio speaks of his experience with this functionality. However I am going to give it a try. I have a tech lined up to do it. If you see a mushroom cloud over the southern horizon, you will know it didn't work in Australia, and the whole reinstallation process is beginning again.
However when the new hardware and drivers are available post DX10 patch and the end of the year, and the equipment is fast enough to run the game well, I am contemplating going back to RTM for the benefits of the better handling of scenery (no verdammt 2 mile pop-up ring).