Best Practice for installing software on Windows:
1. Reboot
2. Install software
3. Reboot
This ensures that nobody left a partially completed install lurking for you that could possibly cause problems.
With Windows, when in doubt, reboot. I know it's not ABSOLUTELY necessary, but in my experience with Windows, it's highly recommended to take the time and do the reboots. Look at it this way: if something goes haywire and the system explodes, you'll spend much more time fixing it then you would have if you'd just rebooted it a couple times.
$0.02