[electrocop]

Not necessarily - as i stated before, if you are happy with Vista and it is still working without problems, the stick with it. You will find Windows 7 very similar to Vista and should be an easy transition, although a few useful features are missing from 7 that are in Vista.
If you have your mind set on upgrading, you will be able to get a Windows 7 disc quite cheaply from the likes of eBay or maybe from an independent computer store. It is worth going for the Ultimate edition as that has the most features. If buying a used copy from eBay, make sure you get the installation key (on a holographic sticker) with the disc(s) to ensure that the key is genuine.

As for the upgrade process, i would suggest a fresh installation, after backing up all your files of course. I would also suggest that you check first with the manufacturer of the computer that drivers for Windows 7 are available.