You speak to the galactic guy out of the HQ .. he leaves and drops a pokeball in which is the storage key...Go and use it in their storage ( same town somewhere near the top left of the city ).. I think the key to the HQ is somewhere in there..:)
By Nekt;)
You find it in the Galactic Headquarters after they capture Azelf, Uxie, and Mesprit.
You will need Galactic key and this how to get Galactic key you will need to talk to a Galactic team mate by the Galactic HQ.
you find it in the galactic HQ
simple answer go to Veilstone city and at the top right corner there is a team galactic building and in front of it there is a team galactic grunt talk to him and he drops the ware house key but here is a catch it breaks in the key hole after you use it and there is more doors so you have to find the galactic key... oh ya and one more thing the galactic key always works!
To get into the Team Galactic HQ in Pokemon Diamond you will need the storage key the Galactic Grunt leaves behind, and the Dusk Stone. If you can't get the key, it may mean you have not completed a mission.
there is this team galactic guy in front of the HQ in veilstone and he would give it to after you talk to an another galactic guy who tells you that he gave it to his partner
Galctic Headquarters is actually the Team Galactic Veilstone Building, but you'll need a Galactic Key to enter most of the doors.
talk to the guy outside of the galatic base he will drop the key on mustake
talk to the team galactic guy in front of the team galactic building.(In veilstone city)
in the vilstone warehouse next to the galactic building
With the Galactic key you can unlock any locked doors in the headquarters.
You find it in the team galactic storage area.