I've completed the majority of the NCR quests and colonel hsu wont give me the key to the NCR safehouse. any ideas?

I had the same problem. Make sure you're LIKED (Not Accepted, idolized is fine) and take off any armor. (I was wearing the T51-B and he wouldn't give it to me, even though it is non-faction specific, took it off and he gave it to me.)

Hope this helps

Vault 69 :nuke:

it says that im a good natured rascal but i will try that

http://fallout.wikia.com/wiki/Fallout:_New_Vegas_reputations

Have a look how the reputation scales work. There is no way to do it unless