my ati all in wonder works wonderfully with mediacom cable. I had it set up on that a long while back... nowadays, I am just doing fta, so I've got it with the signal coming out of the satellite receiver.
One way I think you may be able to do what you are wanting to do is possibly use your satellite receiver's anteanna in and plug the cable in to that... maybe use an a/b to swap from ota signals to cable...
I think, am not sure, but think, that the cable signals should flow perfect through the satellite receiver in to your tv through the receiver's tv out... do a y cord from receiver's tv out, one branch to tv and another to computer... I've got a funky setup at the moment... where the all in wonder is taking signals in from the pansat's tv out, and is also sending signals in to a vcr which is then pumping signals back to the tv in the living room over a long coax run... so I've got two long coax cables going from computer to living room... one to get signal out of there and one to get it in there. With this set up I can see the computer screen on the main tv. Sound doesn't work on main coax for some oddball reason (used to a long time ago), so I get around that by running long speaker extension cables (you can get em at radio shack) from the pc to audigy that's pulling dolby out of the fta receiver. I used a substantial amount of electric tape to make darn sure where the speaker extensions connect outside is waterproof... The radio shack I went too only had something like 20 foot cords. The run that I'm doing is about 80 ft.
I think, if you do set it up, it'd be something like
lnb->satellite reciever's satellite in
ota antenna->satellite receiver's antenna in on A of an A/B switch
cable->cable box->satellite receiver's anteanna in on B of the A/B Switch
Satellite Receiver---->y connector
y connector -->computer on one branch, tv on the other.