Windows service packs–i can’t get them!

Hi,
I just had to install windows xp on a computer and was trying to install office 2007. 2007 requires SP2 or SP3, and i was trying to get them. It says that you can acquire the service packs through the windows update, but i’ve done that 3 or 4 times and it hasn’t gotten any of the service packs. anyone know why and how/where i can get them? (also, i need both 1 and 3, because you need SP1 or 2 to get 3. i don’t know if to get 2, you need 1, so i’m going for 1)
Thanks!