If you buy the upgrade package, then if you ever lose a disk in the future, or otherwise need to reinstall, you'll have to install vista and then upgrade again. If you buy the full package, which will still perform an upgrade if you wish, then you'll not face that problem.

You do not need to do anything techie, and you do not need to format any disk. It will run a check for you and tell you any software it doesn't think will run and any devices that will cease to function. You should pay attention at that point, since you need to understand if anything in there bothers you. Make sure you consider all those issues before proceeding.

It is simple for a non-techie with the one potential issue of non-functioning devices If this happens, and it probably won't, it can be a pain to fix.

In my experience a format and brand new installation is more beneficial, but it certainly is more work and depends on you having a disk you can move all your data & documents to while you do the work. It also means you have to have the installation files for any additional programs you have.

Shout if you get stuck.