I'm looking at building a new PC a piece at a time, starting w/ parts I can use in my current system. A GeForce 8800 GTS is my first move, probably w/ new PSU. I don't expect much trouble there.

The MoBo is where I have zero experience, so my question: if step 2 is MoBo + CPU, what are the chances they'd plug into my current system and boot from my current HD? If it's viable,
I'd do that, then follow up w/ HD + OS.

I'm not sure yet where I'll fit a new box in the schedule, or how much I'll prioritize new RAM--need to scrutinize my current system.

Criticism plz