Vista Ultimate OEM Re-Install...

Ok, I purchased my PC from a local Pc builder. It came with a packaged Vista
Ultimate OEM which I have activated and everything was good for a few
months....

Now, my mainboard has just failed, taking my processor with it and after
consultation with the builder I am going to take the opportunity to upgrade
to an AM2 board and a dual core processor. This means, however, that I will
not be able to use my memory (DDR) or my graphics card (AGP) and so I am
upgrading those too.

Now, I am keeping my hard-drive and optical drives, just replacing /
upgrading my motherboard, memory and graphics card.

Am I going to be able to re-install / reactivate my Vista with these
hardware changes or do I have to contact Microsoft in order to get
re-activated? If I contact Microsoft, what number / department do I call?

Thanx in advance guys / girls.