There are two programs- nLite and vLite that allow you to customize the windows Install disk.

nLite allows you to integrate service packs, hotfixes, patches into the install disk.  It allows unattended setup, which means you can enter your CD key, user information, network information ect... into the install disk so you don't have to enter it while Windows is installing- you just put the disk in, pick the partition and there's no interaction with the installer after that.  You can install drivers, programs, remove Windows components, do OS tweaks etc... into this disk and have it installed every time you install the OS with the disk.

http://www.nliteos.com/

nLite is for XP, vLite is for Vista.  vLite isn't as fully-featured as nLite but it can do basically the same thing:

http://www.vlite.net/

WinPE that I talked about in the LiveCD thread also allows customization of the install disk but it's meant for business customers with large scale deployments.