Unless your HDTV has OUTPUT jacks, you won't be able to get the signal out of it, and share that on another TV.
However, if you are pumping a signal INTO the TV in the first place (like from a DVD player, cable/satellite receiver, digital tuner, etc), then you MIGHT be able to split that output (there are a number of splitters out there for different types of signals), and send one half to the HDTV, and the other half to the Video Sender (which would feed a second TV).
I'm doing something similar to this.
My cable box has multiple OUTPUTS, and is capable of feeding the signal to all of them at once.
I feed one TV with the HDMI output, a second TV with the Component output, and two others with the Composite output (using a Composite RCA distribution amplifier I bought at Radio Shack to split that signal).
If I had a video sender, I could hook it to one of the unused outputs of the distribution amplifier, and send that signal to an additional TV if I wanted.