Is upgrading to Vista a simple process? Yes if it goes right and your software doesn't have problems with it and still works. And the computer you are on has updated Vista drivers available for it.
You would need to buy either the Full Version Or the Upgrade version and you would have to pick the version that suited you, most people seen to want the Premium Version as that includes Aero.
Personally after seeing some of the threads - have a look in the Vista Forum - I wouldn't recommend it just now. Theres too many problems, drivers you need aren't there yet, theres programs that don't work with it and its far too expensive, twice what the US customers are paying.
If you really want it wait 3 months and then look at it again.