this is because you have slipstreamed the Sp1. There are so many pending packages left and integrating more hotfixes will result in more pending packages which must be handled by the Servicing Stack. If you integrated the Updates to a clean MS Sp1 integrated DVD the integration is much faster.
the OEM folder is located inside the sources folder. It contains the bitmaps for displaying the OEM logo and the file which is needed to auto activate OEM Versions.
Use your MSDN DVD mit vLite and later copy the $OEM$ folder from your OEM DVD to your new vLite made DVD and create a new ISO. Now you have a new vLited OEM DVD