Which PSU?

Not sure about the brand but i found this for you

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

its 550w  

oh if your getting a new case buy a atx case with this power supply

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Get this if you can scrouge up a another $5

Most micro ATX cases still take full sized PS2(ATX) power supplies so check the measurements on your power supply, if its about 3" tall then it will take a standard sized PSU which frees you up a lot more options. If it can take a standard sized power supply this would be my pick, its more than enough for your system and much better than that athena unit
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I didnt like the anthena unit but it was the highest wattage for a micro atx psu

Yeah...i checked..its 15cm x 14 cm x 8 cm...