If I take the Yes Man path (overthrow House and take over), am I enemies with the NCR? Or can I ally with any of the factions I want with the exception of either the NCR or Legion together?

You'll receive NCR infamy, but you can still keep a positive reputation with them. Just make sure to do NCR side quests, and ESPECIALLY save the president (you'll become idolized by the NCR for saving him).

cool. thanks. I am struggling with siding with the NCR or doing my own thing. I rather do my own thing but definitely would like to ally with the NCR since I think they are ok

I am on the Yes Man path and the NCR have me flagged at most locations as "not to be trusted", but they are not hostile. They don't give me further quests. Legion on the other hand, watch out. Which is odd since Caesar wanted Mr House killed (and I did).

Out of curiosity, what mandatory actions did you have to do to complete the Yes Man path that pissed off the NCR where you are not to be trusted? Were you in good standing with them initially?

At a certain point in each path you trigger a "failed quest" that just locks off the other main quests. This is the "not being trusted" thing.

It happens after you finish the "side bets" quest, wherein you check in on various minor factions in the game. Once you've made your report to Yes Man about them, you finish "Side Bets" and you're locked in to the independent path.

I don't believe that you lose any NCR cred. You just can't gain any more from that point on.

Actually, I think it happens after you finish "new management" where you kill mr house. Once you install yes man onto the lucky 38 main frame you become locked into the independent path.

On my current character I have side bets finished all ready, but as long as I keep Yes Man in front of the tops instead of inside the lucky 38 I can still choose to side with NCR or the Legion if I wanted to.