a very good piece of advice.
slipstreaming isn't without its minor setbacks as well... when correcting problems with the computer, if certain registry keys have not been updated, the computer can ask you for the windows CD, in a loop, as it wont be looking in the right location...
make sure that entry points to your CD drive letter. Alternatively, you can copy the i386 folder onto your harddrive and point it there.
also, make sure that ServicePackCachePath and ServicePackSourcePath both point to the correct location, usually C:\Windows\ServicePackFiles
Just thought I'd pitch in my personal experience with slipstreaming