Windows licensing ah... been that way since XP liao. If you
bought a system which came with Windows installed, you got an OEM
version. Which is much cheaper and only licensed to run on the
machine you bought.
If you change too many hardware components, windows can detect this
and it will ask you to re-activate. This can be done by just
calling a toll free number. I doubt whether the person on the other
end will grill you to make sure you are not trying to cheat.
Is not really a issue, I think. But to me, Vista is damn
expensive.
Btw, I use XP Pro and Ubuntu.