I can tell you that once you start, you can't stop. The upgrades just keep on happenin'
I would certainly go the Intel way. You want to go with at least a Core 2 Duo E6550 for the CPU and as much ram as possible (3.6gb max on a 32bit)
The SATA hard drive will certainly help you in terms of load times.
However, do not count much on the on-board graphics processor. Upgrade the video card to at least an Nvidia 8800 series.
But of course now you're into $700-800 easy...
FSX and FS9
Level-D 767-300ER,Wilco Airbus pack vol. 2,
Wilco-PIC 737-300 and CRJ Legacy 600
Aerosoft Budapest Ferihegy Airport, London Heathrow and Brussels + AES.