Upgrade Questions X

[Xarulsis]

I'm looking to upgrade my current rig but I have a few questions. Here is my rig right now:

-CPU: (Socket AM2) AMD Athlon(TM)64 X2 4200+ Dual-Core CPU w/ HyperTransport
-300GB HDD + 500GB HDD
-FAN: AMD ATHLON64 CERTIFIED CPU FAN & HEATSINK + 2 EXTRA 3-COLOR LED CASE
-MOTHERBOARD: (Socket AM2)GigaByte GA-M55SLI-S4 nForce4 SLI Chipset DDR2/800 SATA 16x PCI-Express MBoard w/GbLAN,IEEE1394,USB2.0,&7.1Audio
-MEMORY: (Req.DDR2 MainBoard)2GB (2x1GB) PC6400 DDR2/800 Dual Channel Memory
-NZXT PF-500 500Watt Power Supply
-NVIDIA Geforce 7900 GT 256MB 16X PCI Express Video Card

I'm looking to upgrade my system for probably under 600$ but I'm not quite sure what to upgrade. Here's what I think I should upgrade my stuff too:

-AMD Athlon(TM)64 X2 6400+ Dual-Core
- 4gb ram
- ATI HD 4850

How is this system and will it run games well for at least another 2 years? Is my current PSU good enough to support this new setup? I am currently using XP pro, is it a good idea to step up to vista now? Are there better upgrades for my system? Should I wait a few months to upgrade?
Any help is appreciated.

 

[lukas]

i suggest you wait for the new bloomfield quads to come out in a few months, then youll have a bigger budget and more options to choose from.