I tried to edit my sarcastic response earlier but the board was having issues - the submit button was missing, seriously, I'm not joking.
Your answer is almost certainly the crapware/crapletts installed by OEMs on new machines. Vista and XP start up in about the same amount of time. XP may be slightly faster ( by a few seconds or so) but not THAT much faster. Crapware and the stale drivers and useless applets installed by OEM are FAMOUS for slowing boot timers massively. Do a fresh install of Vista and your troubles will vanish.
This is a well known issue and affects XP machines equally. My friends fairly new XP laptop takes about six minutes to get to usability.
I assume this is a Vista install that was on the new machine and you put XP on yourself? If not then your issue is still related to loading software or bad drivers - I assure you Vista loads fast enough when properly configured. Thanks to all the mindless Vista bashing out there everybody now ASSUMES their PC problems are Vista's fault when, as always, the issues are related to software/drivers.
My Vista 64 booted to usability in about minute or so on a regular hard drive. It takes a lot longer now that I have installed a massive amount of stuff but thrn again XP was famous for getting slower and slower over time. So far Vista seems better than XP did in this regard.