Microsoft just recently release the latest service pack, 3, for Office 2003 and subsequent products. And I keep forgetting how to slipstream the packs, fortunately for me I frequent a very good tech site called Petri.co.il run by a Microsoft certified guy named, well, you guessed it Petri.

Office 2003 SP3 (Service Pack 3) Slipstreaming

Office 2003 SP3 Download