Hi Adam:

At least 500W. Remember, if you wish to have an inside-compute RAID with 2-4 HD as well as the CD and all the USB power consumption, it's a good thing to get a great power supply. Heck, at ebay you can get a 600w power supply for as little as $30 (shipping included). You can even get fancy and buy a $16 one that glows in the dark (this guy sells 3, so you can save on shipping http://cgi.ebay.com/Power-Supply-60...949QQssPageNameZWDVWQQrdZ1QQcmdZViewItem ). This one has dual fans, and no lights (lights tend to short)- http://cgi.ebay.com/PowerStar-600w-...949QQssPageNameZWDVWQQrdZ1QQcmdZViewItem . Here's another multiple-item seller offering good shipping options- http://cgi.ebay.com/Power-Supply-fo...WDVWQQrdZ1QQcmdZViewItem#ShippingPayment