Both the -700 and -100's have this ability.
you can only go back as far as the time you tuned to that perticular channel though.
Use the top circle of buttons on the remote.
Provided you have the HR20, and not a H20 yes this should work fine.
For some reason, it will not pause, rewind live content from the channel you are watching. It's works OK with a recording - seems bizarre and/or defective. I'm running f/w rev 0x18a - any known issues with this release?