Is it possible to plug a Thunderbolt cinema display into a Mini DisplayPort-equipped Mac and have it work? This question suggests that it's possible and that it's pretty much the same cable, but I don't see any explicit confirmation anywhere.
The spec page for the display implies very strongly that Thunderbolt displays will only work with Thunderbolt Macs.
This happens to concern me since I own a previous-generation iMac (pre-Thunderbolt) and really wanted to have the option to use it with a Thunderbolt display. So I asked the guys at the Apple Store.
The Apple Store told me no, it will not work on a non-Thunderbolt Mac.
Sorry to be the bearer of bad news :(.
Plugs are the same, cables are not. The thunderbolt cables contain chips and firmware.
I haven't used the new Thunderbolt display, however I am aware of the following:
MiniDP Macbook -> MiniDP iMac 27: works fine. Thunderbolt Macbook -> MiniDP iMac 27: works fine. MiniDP Macbook -> Thunderbolt iMac 27: does not work Thunberbolt Macbook -> Thunderbolt iMac 27: works fine.
This is in my experience and confirmed from various Apple KB articles. So I believe it's likely you won't be able to use the Thunderbolt display on a MiniDP machine, as that is certainly the case with the iMac 27" models.