couple of ways you can do this, main thing is you need to have is a hard drive image program and a way to hook up your 500g drive to the computer as a second drive. You do an exact image of your current hard drive to the new one, swap hard drives out, and then edit the data partition in vista with only the 500g drive in the computer.
Edit: lol forgot the other way...you could take both drives to a computer shop that has a drive imager and do it that way also, but they may charge for something like that.
Edit: lol forgot the other way...you could take both drives to a computer shop that has a drive imager and do it that way also, but they may charge for something like that.