Phenom x6 @ 2.8ghz
This is perfectly fine.
GIGABYTE 890GPA-UD3H
Again, no complaints here.
1GB X2 KINGSTON HyperX Blu (will add 2 more gb)
Here's your problem. You really should have 2GB of memory MINIMUM, 4GB ideally. Also, try to get matched pairs so you can run in dual channel mode. If you're already running 512MB sticks, two 1GB sticks aren't a horrible plan, though 2x2GB sticks (4GB total, and ditch the 512MB sticks) would be ideal.
COOLER MASTER CM690 mid tower
Good choice.
APEVIA ATX-JV650W
This power supply is junk. It'll probably be ok for now, but as you start to overclock and if you add a high-end graphics card, you could be asking for trouble. I'd suggest upgrading to a brand that's known to put out good quality stuff, such as Seasonic, Corsair, or Antec. Especially with power supplies, you pay for quality.
Western Digital Caviar 320GB+another seagate hard disk 320GB
You could get a performance boost here by going with a newer, faster HDD (such as the Samsung 1TB F3 or Western Digital 1TB Black), though it's not a huge concern. A Solid State Disk (SSD) would make a gigantic difference, though the price is also somewhat prohibitive.
win vista
Windows 7 would help in terms of speediness, but switching isn't really a necessity. I would upgrade the memory, power supply, and hard drive before upgrading to Windows 7, personally.