Looks like a good system there Longam. It should handle SH4 just fine. And it leaves you room for improving the system with upgrades when the prices become affordable like a Core2 Extreme processor, or a better video card, and ram.
With Vista you may wish to go here:
http://www.blackviper.com/
It will help you set up vista to run better than the stock settings by showing you what you can turn off to reduce the resource gobbling power of vista.