Originally Posted by occam
If one or more of the devices on your system are using "blacklisted" drivers, then you should wait a while and check back on Windows Update often.
Microsoft is currently working with hardware vendors to have these drivers replaced with ones that do not get in the way of Windows Update downloading SP1. For the awhile, these drivers will be listed as optional updates, and a little further down the line, they'll be elevated in importance to "critical" level.
When your has all the correct drivers, then SP1 should show up on Windows Update. If you choose to download and attempt to install the standalone version of SP1 (434MB or 32 Bit, and 726MB for 64 Bit), then may I suggest you first make a backup of all your important data before proceeding? At best, you'll lose functionality of those devices after installing SP1. Worst case scenario is you hose your entire system, for which I have not yet heard any reports, but rather safe than sorry.
Have you tried going to your hardware device manufacturer's website to see if there aren't any updated drivers available that may/may not resolve the SP1 block on Windows Update?