Do you have money? Do you plan on playing Skyrim? I would be getting a computer for Skyrim first then you would know you can play New Vegas. If you don't plan on getting Skyrim, and just want to play New Vegas, then any computer that is within 2 years of age should run NV really well. My laptop can play Fallout 3, but that was after a year of playing on the 360, I wasn't sure if it would run or not. For NV I have it on the 360 since I didn't want to chance it.
You should be able to get a computer now for about $500, maybe $600 with monitor to run NV at max settings. If you don't want to build one yourself, look around, try Future Shop/Best Buy or what not. If you have the money and don't mind spending a bit more money like $800-$1000 then get one that will run Skyrim so you have no worries for both game then, as I said.