I dont mean to be a killjoy but to get good performance with front row I think your going to have to not go with a apple card with ADC. I would suggest a Flashed card and the be all and end all card for cubes is the nVidia 6200 or if you want to go a little cheaper there is the 5200 which will be pretty good. the 6200 is nice because it has a built in temp censer and it doesn't run too hot. So you may want to check out http://themacelite.com/
as all the flashing guys hang out there. You can check out ebay too for whos selling them and remember only buy from the highest rated sellers. I would offer to flash it for yea but I dont have a compatible mac to test the card on. Also I forgot to mention you need a card that supports Core Image which the 7500 and Geforce 4 do not.