The above is very good advice, but we cant really tell you what you should do.
Clean install would be far easier, and less headache, although I wouldn't recommend it unless your up for a challenge. it IS possible to do an install-repair after swapping the hard drives to the new MB. This will take longer, and will end up with more data on the disk from the OS install, due to the left-in bloated driver scripts. I've done it, but it was 3 hours wasted of my life.
Clean Install +1