ok so i went to Jacobstown(sp?) to get rex fixed and afterwards Marcus asked me to help him get rid of some mercenaries who have een harrasing the town. Well after failing the speech challenges i went ahead and started shooting after they were all dead a get a message saying the NCR hate me...so i was just wondering as to how i get them to like me again?

If you do sufficient quests for individuals you can improve your reputation but it will always be tarnished even if you get it back to be largely positive.

So am i going to have to revert to a later save point? I saved the game right before i started shooting in case something bad happened...

Did you deal with Benny yet?
If you have not delt with Benny, just play the main quest more.

Also there's a easy way to deal with the mercs, just pay them off.

I havent gotten the platinum chip yet but i have talked to him before

So you already got a pardon from the NCR MP?
If so I would just reload if you can.

yea i already got a pardon. To tel the truth i really have no clue what im doing in this game...its alot differant than Falout 3....