I found this in a few different places around the 'net - hopefully it's helpful:

Restore Declined Windows Update Reminders

Windows Update scans your computer and provides you with a selection of updates that apply only to the software and hardware on your computer. The updates include security fixes, drivers, critical updates, and the latest Help files to keep your computer up to date. If you choose not to install a specific update that has been downloaded, Windows deletes its files from your computer.

• Click Start, click Control Panel, click Performance and Maintenance, and then click System.
• On the Automatic Updates tab, click Restore Declined Updates.

If any of the updates you previously declined still apply to your computer, they will appear the next time Windows notifies you of available updates. You can always install specific updates from the Windows Update Web site, by opening Windows Update in Help and Support Center.