Vista, like its predecessors will be fast when you first boot it and for a few weeks after but like every other version of Windows will get slow, here are some tips to help curtail that but you will still have to do the occasional reinstall to get all your performance back.
In order to make Vista boot faster, the only thing you can really do at this point is defrag the hard drive. After opening and closing files all the time, these files become spread in fragments all across the hard drive, increasing seek times, defragmenting puts them back into one contiguous spot and some utilities even have options for optimizing boot by placing the boot files and startup programs as close to the start of the drive as possible.
Windows XP users have the option of using BootVis but if you don’t know how to use that tool, don’t, it can really mess up your system if used wrong. Sadly, it does not run under Vista which is a real shame because it’s an awesome utility and really does something to improve XP boot times. Used with TuneXP (also not compatible with Vista) it’s a lethal combination for shortening boot times.