When I installed Vista (clean install) on my laptop it asked for a computer name – which I gave as John.
After install (user account was enabled) I had a user called John, but I didn’t like this user’s name so I renamed it Sam.

I now notice my personal directory is called Sam but in C\Users I have a user called John and it seems identical to my personal drive called Sam. I would like to change c\user\John to Sam to eliminate confusion. What is the best way to do this? Can I just rename it.
I am thinking there are a lot of registry values with the name of John which would need changing?
Both Sam and John are administrators.

Thanks

go here and change the name for the computer.

Change Your Computer Name in Windows Vista :: the How-To Geek

go here to change the registered owner

Change Owner v1.0 | Windows Vista for Beginners

I am not sure which one is the one that you need to change....but one of them will do the job that you require!