Yeah, I can see mine in the NVidia thing. i went to Display/Setting/Advanced/ and then on the next windows I click on GeForeceFX5600 (The name of my card) And then this thing showed right up showing the temp. I imagine your will be very similar, just replace GeForceFX5600 with ATIRadeon9800. Thats just an assumption.
On another note, my GPU is at 68 Degrees celsius. Think thats too hot? I have water cooling, but I dont have a GPU water block. Only the stock fan. I used to have one of those PCI fans that fit into the pci slot and put a fan under the card, but it burned out.