I have 3 quests that require me to enter Nellis Air Force Base, however the guard at the gate won't speak to me. He stands there, watching me.

Any possible ways to work around this?

I, too, am having this error. From a quick Google search you can tell we're not the only two having this error. I have not been able to find a way around it unless you are using a PC version. I have done almost all of the other quests I have in my Pip-Boy and now it seems my game has been halted. Every day when I log into Xbox Live I pray for a patch. I hope that by posting it on the official website, maybe they'd address it soon...hoped.

I had this problem as well and found a recently added answer on Yahoo! Answers. I just confirmed that it works, I hope you're as pumped as I am:

1) Go to the gate of Nellis Airforce Base, either by fast-traveling or by working your way through the bombardment.
2) Save so that you are right at the gate for easy reload - this make take a few tries.
3) Go into VATS and disarm one of the roaming patrols. The (non-glitched) guard with the rocket launcher seemed to be the easiest. When successfully done a fight will ensue, but holstering your weapon will end the fight, and the glitched out guard who SHOULD be letting you in will FREEZE in whatever position he was in when the fight ended. Get the fight to end with the guy near enough to the fence, and you can talk to him through it. He will be surprised/impressed that you reached the base, and call a woman who teleports you in.

It took me almost 30 minutes, but, by god it worked. Finally!