For clarity: This is a requisite update file; an update to your system you need to get before SP1 can be installed when released.
Quote:
The problem doesn't actually affect SP1, which was considered finished and done at the beginning of February. However, Microsoft decided to delay its release until mid-March, irritating some users. If KB937287 installs on the user's computer without the reboot bug, then they can install SP1.
