dude, I have only 512MB memory, and it works as fast as it can get. I don't defrag it, and it opens the program in one sec, and My video card sucks ass too.
It seems to me that the slowness indicates that you probably have spyware/malware running in the background. If you are running XP, download the Microsoft spyware beta and I'll bet you'll find the culprit!
There's no reason that powerhouse PC should be taking that long. 512 is MORE than adaquate to boot up and get your OS running. It's got to be something running in the background.
When you upgraded your processor and motherboard, did you do a fresh install of Windows? If not there may be some old drivers conflicting with your new setup. Always worth a fresh install when you do a motherboard upgrade.