Others have already touched on the general plan -- splitters vs. diplexers
and so forth. Assuming that you're taking the signal from the DTV unit and
splitting it to your systems, you should be fine.
If you decide to actually set up additional DTV receivers throughout the
house, you will be subject to the $4.95 per unit fee from DTV. The units
will be nothing more than pretty paperweights until you activate them with
DTV so expect to pay the monthly fee if you want to use them. In order to
use them though, you'll need to buy a multiplexer and multiple LNBs for your
satellite dish -- you can NOT simply split the satellite signal. The
multiplexer will ensure that the signal remains even across the connections.
A single LNB on a dish, run to an internal multiplexer, can successfully run
two feeds with no problems. A dual LNB run to a multiplexer can run up to 4
without issues. TriLNB could knock you up to 6 or so as well. Single and
dual LNB configurations run from a single dish with a single LNB mounted on
it -- tri LNB has 2 mounted on them and will likely require a special
purchase (i.e., you won't be getting them at your local Circuit City). I
currently have two receivers with 2 feeds on each that hook up to a 4 way
multiplexer which in turn goes to a dual LNB -- signal strength is typically
in the low 90% range.