I found this in a few different places around the 'net - hopefully it's helpful:
Disable Automatic Windows Update
Windows XP is configured out of the box to routinely scan for and download updates to Windows XP automatically. While this can be somewhat convenient for those with very fast Internet connections and those who would otherwise forget to check for updates, it can be a nuisance for the rest of us, who are still using 56k or, even worse 33k modem connections.
- Open the System icon in Control Panel (or right-click My Computer and select Properties), and choose the Automatic Updating tab.
- To check for updates manually, open Internet Explorer and select Windows Update from the Tools menu.