It kind of depends on what else you have in your computer being powered by your power supply. But I would think 250 Watts is too low. Get a good power supply by Antec, Enermax, Thermaltake, or some other name brand. I would get at least 430 Watt. This is what I just bought:
http://www.newegg.com/app/ViewProduc...153-007&depa=1
(Thermaltake W0014 Silent Purepower 480W )
I like it a lot. As far as changing your PS, it's not hard. It's just 4 screws and a lot of cables. Good luck!