I don't have time to give you step by step instructions, but Norton Ghost will make a mirror image of your drive so that you can boot from it. Hope that helps.
Is Norton Ghost free?
EDIT: Never mind; it isn't. So is this what I do:
1. Attach new drive via external enclosure
2. Use Ghost (trial) to mirror contents of old drive onto new one
3. Swap drives and boot from new one
WOuld that work?