As always, you must assemble certain ingredients and configure your computer properly before getting down to business. Follow these steps:
Boot into Windows (any version). This can be a copy running on a PC, via Boot Camp, or in a Parallels, Fusion, or other virtual machine. The copy of Windows you use for creating a slipstream CD does not have to include Service Pack 2 or later.
Obtain a copy of the latest service pack (SP3 as of early 2009). You can do this in either of two ways:
Download it from http://www.microsoft.com/downloads/details.aspx?FamilyId=5B33B5A8-5E76-401F-BE08-1E1555D4F3D4. Be aware that this is a 316 MB file; if you don't have a very high-speed Internet connection, the download will take a while.