They are both listed for $299, but deals may be available.
Differences:
-100 runs cooler.
RF remote works better on -700 (internal antenna) than on -100 (external antenna).
-100 had both optical and coaxial digital audio.
-100 has second network port (I don't know if it is functional).
-100 may have a slightly larger hard drive (I haven't verified this).
-700 has newer software if you participate in CE program.
-100 made by Thomson (RCA); -700 made by Pace.