Nope just a regular old power supply will be fine. If you run 2 cards, you just need one that's a little more powerful, closer to 600W. My OCZ Modstream 520W is an awesome PSU and i'd highly suggest it to you. OCZ is just a great company that produces products with high quality and reliability.
AMD 64 3200+ Newcastle@ 2.2Ghz
1GB (1x1GB) OCZ Performance Series
ATI X700 Pro 256MB OC\'d 475/525
OCZ Modstream 520W
Samsung 914v 19\" 12ms LCD
SB X-Fi w/ Logitech Z 5300e