Vista User Directory

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