I had no issues at all slip-streaming Windows 7 SP-1, this little program will do that and only that, if thats all you want, but you can also customize your installation as well.
I tweaked mine and have it set as a complete silent installation.
Getting started with RT Se7en Lite
RT Se7en Lite is developed by Rockers Team to customize windows 7 operating system and to make it lite. You can add wallpapers, Icons, themes, integrate updates, drivers, language packs, applications, remove components, enable or disable features, unattended installation settings, bootable ISO and USB creator , etc. It will be very easy to operate and changing the style of your windows 7 operating system.http://www.rt7lite.com/
You have to use, RT Se7en Lite - Beta (Build 2.6.0) for slipstreaming, its a beta, but as I said I have done it already and it works.
Keep in mind though, for those using daz or hazars activator, its much more difficult to work with a slip-streamed SP-1 disc, clearly they patched some holes:)