You just create an answer file then insert it into the ISO in the i386 folder as WINNT.SIF, using your favorite ISO editor. (UltraISO for me).
Once you have the answer file the way you want it you can resue it and give it to friends, just modify the admin password and CD key first.
Slipstreaming is also easy, or you can just request an SP2 CD from microsoft. Or copy one someone else made, as long as its the same version as the one you own (Home/Pro Retail/Corp/OEM) and you are still using your legal CD Key you are fine.
I would only use nLite if I wanted to add/remove drivers to the CD so that I didn't have to press F6 durring install.