i would think that you would want to max out the ram, prolly get a 150gb hard drive. i would also think an HD tv, but you dont need it. or you could go with the standard hard drive and a firewire external hard drive
The lowest spec mini is specced higher than an ATV.
I have a 1.66GHz Core Duo Mini with 2GB RAM. It handles everything fine, but then I don't have a HDTV.