How many watts i need to work that card?

AMD recommends a 400 watt PSU which means is should run on a 350 watt one, will use about 65 watts at max power.

yeah, i ran one on a 300W cheapy psu just fine. It's better to have some head room though. Also it's only the 12v rail(s) that matter. If you don't have the psu yet, one of these would be best:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
They are both very good but not modular, post if you need a modular recommendation.