If you don't have a domain, then the most straightforward way is probably to download the network installation version of the service pack, put it in a central location (i.e., a file server or even a permanent CD) and then deploy using sneakernet at each server console.
EDITOR'S NOTE: For more information, register for Jonathan Hassell's webcast New security enhancements in Windows Server 2003 SP1, or view the following checklists in the series:
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