I am doing the quest "Render Unto Ceaser" and while I am doing this quest currently, I need to be at Hoover Dam, in which I am, but I go to where all the NCR are and I get killed by the Rangers, then I decided to wait for the Vertibird... but it didn't show up while I waited at the bridge... assistance please?

You have to talk to that other agent(forgot his name) after you talk to him Kimball will show up. If I were you go back to an earlier save and get at least two stealth boys makes the mission alot easier.

Well, I did talk to Cato I think his name is, he ran there and I followed, then I waited and waited for Kimbal but he was a no show, I couldn't even get close.

You have to talk to him again to make Kimball show up.

Well, I need some assistance because I am Vilified from the NCR and I didn't kill them, I think it's because of the Legion... but this quest is at Hoover Dam...

I'm not playing 'Forum Cop', by any means. You may get a more detailed response if you ask a Mod, to move tour thread to the other forum. Discussing the details of a quest will help you out.