HardMac is speculating that the next generation AppleTV 2 (or 3?) might use one of the new System on a Chip (SoC) designs Intel announced this week at CES.  Currently, Apple uses a standalone  1Ghz pre-Core Intel chip for its AppleTVs.  According to Hardmac,

They plan to release in Q3 2008 the Canmore, an x86 processor-based SoC supporting audio 7.1, hardware-decoding for high-definition video up to 1080p and advanced DRM management.
In summary, all functions required to build a new and more powerful Apple TV which could then become independent of any computer to get access directly to movie catalogs available on the iTunes Store.

According to Intel, the Canmore line shouldn't be ready until mid to late 2008.  Apple, readying iTunes movie rentals won't need too much - if any- more horsepower to download and play rentals on the AppleTV.  However, if the device is to operate as a standalone device, a speed bump may be in order.