Is it possible to get mr house and the ncr to ally up? Or does it haveto be ncr, legion or house that wins in the end?

No alliances between the major factions.

Originally there was going to be an option to annex Vegas with House still alive, but it was cut.

Hm, to bad. Thanks for the quick answer.

You can bypass a science, barter or speech check of 100 for the Mr. House questline. If you do that then you can complete the game on Mr. House's side without killing a single NCR person.

Oh, i have 100 barter, that would work?

It wont end the game with mr house in posseision of the damn? but the ncr gets it?

No, Mr. House gets the dam, but the NCR will retreat without losing four veteran rangers and their general