The only proviso I would add is that, with this method, there are certain situations where you can wind up with GRUB getting "lost" at boot time. This is because you change the physical drive order in the BIOS, but the OS is still smart enough to "know" the difference between, for instance, hd0 and hd1. Worst case scenario you wind up staring at a GRUB prompt that wants to know where the loader is. You just change the drive to the other one, and the boot will proceed normally. Then, while you're up in that session, you go into the configuration file and change it so that it uses the correct drive / partition on the next boot.
This was a problem with Ubuntu and Linux Mint previous versions. Not sure if they've fixed it yet.
Be CAREFUL when doing the install. The Ubuntu installer used to be really dumb about this, making it very easy to wipe the drive on which you intended to keep Windows. Bear in mind, you must change the boot order BEFORE you install Ubuntu (so that the 80 GB drive is first), and then choose the installation location from the custom installation process. It will NOT be the default choice. At least that's the way it was 1 version ago.
I recommend visiting the Ubuntu forums to get the latest poop on using this method of installation. I still prefer it to using GRUB as the boot loader for both Vista and Ubuntu, but it is more work up front. More work up front, but the two operating systems are then not affected directly by each other in normal operations, and you can remove one or the other with no hassle.