well what i did is i just plugged my old hard drive into my mobo (when the systems off ) and then went to my computer and moved the files i wanted to from C:\ to D:\
if you want to change which one boots, you have to set the jumpers and/or BIOS to let it know which one is the "slave" and which is the "master"
ha, i'll probably need to ask some question in a few months too... im finally about to get my rapter 150gig
Buy Norton Ghost, there is an option on the bootable CD that allows you to copy one entire drive to another. It just copies everything exactly, which is what you would want if you are upgrading to a new faster or bigger drive. Hope that helps.
If you have western digital hard drives they have a tools CD that can be downloaded that will ghost your new drive from the old. It has always worked for me. I'm not sure if it is compatable with non-WD hard drives though: http://support.wdc.com/download/index.asp?cxml=n&pid=999&swid=1