have a nose around here click here it's quite good.
I did an upgrade from XP to Vista home Premium. it took about 45 mins with several reboots and times when you think it's stopped when it has not.
Make sure your XP is fully up to date pop in the DVd and have a cup of tea handy. it's really useful if you are connected to the internet during install, Vista will trot off (after it asks you) to get updated drivers if the are needed. there are some handy Vista sites to look at (other than here of course!)