Anandtech has gotten its hands on an Apple TV unit and dissected it for our benefit. Some of its innards:
1) 40 GB 2.5" laptop hard drive
2) nVidia GeForce Go 7300 64 MB, with Turbo Cache support
3) Intel 945G chipset
4) ULV 1 GHz Pentium M Dothan?
5) 256 MB RAM
I wonder if Apple is utilizing the GeForce Go 7300 for H.264 decode assist.
TechRestore also has some pictures.