I know this sounds like an add but since Jamie can post about re-installing his OS I can post about NOT re-installing my OS 
Besides, this software is free for 15 days and it's not like you're going to take more than 15 days to clone a drive.
Vista is working fine and I didn't want to re-install everything so when I got my new WD6400AAKS 2 days ago I decided to use an HDD cloning program for the first time ever.
Since people where having problems getting cloned Vista boot drives to boot when it first came out I was glad to see that Acronis came out with something simpler than their other more full featured disk imaging products named Acronis Migrate Easy 7 that is perfectly Vista compatible.
Basically I just ran Migrate Easy on my 250GB drive that also has Windows on it, made the new drive bootable withing Migrate Easy and then pointed it to the 320GB as source and 640GB as destination. After quite some time I had a 640GB drive that's a perfect clone of my 320GB drive.
Migrate Easy 7 is as simple as it gets.