I'm not sure it can be done...and enjoy the game at the same time.
The game will get a free DX 10 upgrade when(soon after) vista is released (so says MS).
The game will need a high end vid card for top visuals and smooth gameplay.
You can base it around the e6400 CPU
http://www.gamespot.com/pc/sim/microsof...imulatorx/news.html?sid=6159742&page=2
"The graphics are for the most part better. The program is HUGE, over 15GB for installation from TWO DVD's. However, whoever wrote the specs for the program must have been on some really good drugs. 1GHZ processor, 256 MB ram on XP, and a 32 MB video card would be cripplingly understated. I have a 3000+ athlon xp, 1GB of memory and a Ge-force 6800 GT at 1024x768 res with medium settings and it still hitches and crawls whenever the plane turns"
15 gig!!

(not bad considering they intially had a terabyte of real world data)
edit: here is another one that shows the true power needed:
"I have been having fun with FS9 for some time and then decided to purchase FSX. This is where the expense started. I thought I had a resonably high end system but no way would FSX run very well on it unless I turned every thing right down. This of course defeated the object as the graphics then resembled FS9. So I went out and paid £1300 on a new PC. An Athlon AMD 64 dual core processor 4600 with 2.41 GHz and 2 Gb of ram. It also had an Nvidia 7950 GX2 1 Gb graphic card. Can you imagine my disappointment when even this machine struggled with FSX!"
http://www.amazon.co.uk/Microsoft-Fligh...luxe-PC/dp/customer-reviews/B000GBPLYI