This blog article will guide you through the process of slipstreaming SP1 into Microsoft SharePoint Foundation 2010. The process for the non-foundation edition is identical with the exception of the file names and the actual service pack file.
Extract the SharePoint installation files into the D:\sp2010 folder::
SharePointFoundation.exe /extract:D:\sp2010 /quiet
Extract the SP1 files into the D:\sp2010\Updates folder:
sharepointfoundation2010sp1-kb2460058-x64-fullfile-en-us.exe /extract:D:\sp2010\Updates /quiet /passive