The Slipstream functionality in Service Pack 1
There are 2 different procedures that allows you to patch the original SQL Server 2008 product
Procedure 1: Basic Slipstream steps:
These steps are better for a single installation as the steps are simpler since you don't need to copy the original media locally, all SP architecture types do not need to be download and there is less of a chance to make a mistake.
Procedure 2: Creating a Merge (slipstream) drop:
These steps will guide you in creating a drop from where can install SQL Server 2008 SP1 in a single step.