Go to Goodsprings mand find Billy Cob. He can give a quest to kill Ringo (he has Caravan Cards).

Kill him and return to Billy. Then, talk to him and you will score neutral reputation with Blasters.

Now,select the option "It's all I can do. Let's secure Goodsprings." and follow Billy.

When all of Goodsprings Warriors are eliminated, you will score friendly Reputation with Blasters, and the Goodsprings is yours!

Note 1: If you do it, you will score bad Karma and bad Reputation with Goodsprings.

Note2: You will need to kill all of Goodsprings people (including Sonny Smiles and Zabey-Pit), not including Billy Cob and Blasters.