The original trio of Apple Studio Displays (who differ mainly in their inputs and a few other options) do require an AC adapter. It's from the awful beforetime. Before the Dell Ultrasharps were invented.

Here's the adapter from a reseller: http://www.welovemacs.com/92241661.html

If I'm remembering correctly, the power adapter is a relatively common point of failure on those displays (along with the height-adjustable stand) and it seems like these days, finding one without those two items is way easier than finding one with them. (like here: http://cgi.ebay.com/270819267862 )

Here's the hack JT was talking about: http://hackaday.com/2010/11/03/normal-connectors-for-apple-studio-display/

That's an entirely different ballpark though and you shouldn't have to do that because the power and video and USB aren't integrated into one cable, like on the newer ASDs. Getting a pinout for the AC adapter should be all you need, and if I remember correctly, the connector is more standard than you think. (But I don't have one so I'm actually not completely sure.)

Good luck -- getting one of those to work properly could potentially yield a very nice looking setup.