Actually all of the PCI slots are "special" slots. The standard PCI slot looks like the one the video card is in. However that slot runs at 66MHz where as a standard pci slot runs at 33MHz. The other slots are 64bit PCI slots that run at 33MHz. If you plug a normal card into one of the 64bit slots it will act like a normal 32bit slot. If you were to plug a video card into the video card slot it would run at the faster speed which it may not be able to handle. I think the Radeon 7000 PCI Mac Edition can run at either speed, but I am not 100% sure. If it can, definitely put it in the same slot as the current video card as this will increase performance. Hope this helps...
Edit: I looked at a picture and the 66MHz slot is notched differently from a normal PCI slot. If the card has a notch closer to the backplate at the one end then it should work fine (it should also work fine if it has 2 notches). You might want someone else to confirm this though.
