Are you sure the 1st hard drive (the one with windows loaded) is set to primary boot in your bios and you don't have them mixed up?
When you have a new system and you put in an old hard drive with an old windows installation from a different computer, you will definitely run into problems with it recognizing hardware at some point because of previously loaded drivers etc. I always use a freshly formatted drive when installing windows on a new computer, that way you have a clean slate to work with.
If you do want Win7 when it comes out but need an OS right now, I would suggest using the Windows 7 RC
until then. It is a free to try beta version of the upcoming OS, but many of the members here including myself use it day to day and it works great. It lasts until 2010.