A lot of the times when people dont get a Vista disc to format with you will find a partition on the drive that returns the laptop or pc to the original state it was in when it left the fatory so buy finding that and running it, it will be exactly as it was the first time you took it out of the box.
Some may find this as a partition on My Computer and others may have to restart and press escape or delete as it fires up but so if you didnt get a disc and you can find system recovery you will be able to do it this way just like Chris said.
BUT........When you have run it and everything works do a back up of everything using Windows. That never seemed to matter to me untill I blew my hard drive, then finding out that you dont have a disc to reinstall Vista, so your replacement drive is empty, so you dont have Vista to make anything work!
Daz, February 2009