If you have a Windows computer handy, then take a look at nLite. What it essentially does is takes the Windows data off of your SP1 disc, combines it with SP2, and then gives you a SP2 disc image. This is what Dysfunction was referring to as slipstreaming.
A neat part about slipstreaming is that you can also add and remove other things. Say there are parts of Windows you don't want installed at all, just remove them. If you want to add in every security patch ever released, you can throw those in there too so that they're installed at the get go instead of having to download all of them after installation.