TD,
The site 'spanners' suggested works for me OK but I seem to remember that MS said that to load SP3 on to a single computer was unnecessary and providing automatic updates is on it will load only what a single machine requires - there is a piece to that effect. It is a large file - some 316mbs.
Don't know if it helps but thought it might be worth knowing. I checked my machine out and the K updates for SP3 are in fact loaded - I didn't know that I have to say!!!
PPP