Hello, I recently purchased a RCA DVR80, which is a Directv/TIVO
receiver.  This receiver is a 2 tuner receiver which means I can
record to programs at the same time.  For this receiver to properly
work, I've been told that I have to make 2 cable runs from the
Satelitte Dish to the receiver.  I have a 3 LNB Dish (3 satellites)
with 4 outputs.  I only have this receiver, so I know there is room
for the 2nd tuner.  However, I don't want to make the 2nd cable run
since it will require having cables running all over the floors and
walls (I can't get into the inside of the walls anymore).
My question is can I use a special cable splitter to use the 1 cable
run to my receiver, and split it there into the 2 tuners (Please note
that I don't want to make another cable run from the dish itself??  If
so, where can I buy it??

Unfortunately, you can't do it with a single drop.  The cables coming
from teh LNBs go to a switch installed with the dish.  In your case,
this is a 4x3 switch.  It has 3 LNB inputs and 4 outputs.  I have the
same setup.  Different satellite channels are received from different
satellites and thus are received through the different LNBs.  Your
satellite receiver sends a signal back to the switch to tell it which
LNB to tune to based on the channel it wants to receive.  So if you
really want to use the 2 inputs and record and/or watch 2 different
programs at the same time you need two drops.  Some people will tell
you that you can split the wire, and technically you could split the
incoming cable and put a DC block on one of them, but then the one
without the DC block would control the switch and the other would
receive the wrong channel - or nothing - when the first one switched
to the wrong LNB.

If you send it to a splitter and DON'T use a DC block and the splitter
doesn't block DC, you could do some damage to the Tivo unit.

Basically, it won't work.

Now you CAN multiplex an antenna signal onto that cable in order to
get off-air local channels.  Those are available at any electronics
store, maybe even WallyWorld.  You don't need the real expensive ones.
 The signals are digital.  Either they work or they don't.

I don't know your house situation, but why not run the cable along the
outside wall to the spot closest to your Tivo?  Then drill throught
the wall there.  Should not be too difficult.

Regards,
Jim C.