if you're doing slipstreaming anyway, you should consider tossing in the
RyanVM Integrator post-sp2 update pack. Pulls in all the windows updates since sp2, up to current. Currently that's something like 70 patches, and will save you like an hour of downloading.
There's also add-ins you can use to pre-install software, and switchless installers for common apps (like acrobat reader and the sun jre). In my sysadmin role, that pack has saved me probably 15 hours of boredom over the course of the last 4 or 5 months.