Windows Vista activation questions and reinstalls/formats

I am a hardware enthusiast who upgrades and maintains is hardware maybe 3-4
times a year. Include motherboards, hard drives ect. I also clean my system
at times with a full format due to unforseen issues ((such as viruses that
sometimes occur))

I recently bought two full copies of windows Vista Ultimate. ((Full
Installs)). One for my laptop and one for my desktop. I have heard alot of
incorrect ((or correct)) information about activation limits. Ect. And I am
wondering how much of this is true? I have a new hard drive in 2 days which
will require a full reinstall and reactivation of Windows Vista. Will this be
a problem? Am I limited on how many times I can do this?
What about my laptop if it gets a virus? Will I have to worry about it not
activating due to my already activating it?

I am asking these questions because I simply dont know what to expect when
these situations arise. I payed "alot" of money for two copies of windows
Vista Ultimate and I'd like to assume I have the flexibility to do full
reinstalls when my hardware changes or I am forced into a reinstall for
whatever reason.

Chris