Renaming a MOSS server is meticulous job. If anything goes wrong along the way chances are that you need to reconfigure your whole MOSS environment.
Here are the steps to take, and the order in which to take them if you want to rename a server that has MOSS already installed and configured on it:
*** NOTE: Use only letters, digits and minus for the machine name (so no underscores), max 15 characters.
Change each alternate access mapping for your MOSS/WSS deployment in Central Administration:
Open Central Administration, "Operations" Tab, "Alternate access mappings" link
Modify each mapping item to reflect your newly chosen server...