Yeah I'll mirror what Luca said, the 9650 is the card you want, should cost no more than $150 depending on your luck with ebay, and if you have a g4 you'd tape pins 3 and 11 from the metal back end (where the plugs go), plus it'll be able to drive it at full res.
The Cinema display will work on a non-dual-link card though, There is no physical difference in the plug on a dual-link jack and a single-link jack (the center 6 pins of the plug simply aren't used), though as an interesting side note, the reason ADC didn't continue was apple's short-sightedness to not realize they'd better keep the extra 6 pins [which they ended up using for USB!] for a video signal, whoops!