No problem, welcome to the forums. I'll start with the first part of your question, about what you need to add a regular reciever to the existing TiVo unit you have. First I need to know exactly what kind of dish you have. You said it is a dual LNB but then said oval so I'm a little confused. How many "eyes" does your current dish have? 1, 2, or 3? If it only has one "eye" then very simply, the two lines coming from your dish to the TiVo, at some point will need to be cut, and a 3x4 multiswitch inserted at the cut point. If the room you are adding is next to where your TiVo is currently located, you could insert the switch right behind the TiVo and go through the adjoining wall with the new line. Or if you have a unfinished basement/crawlspace and your other room is on the same floor, same thing, splice the switch into the lines behind the Tivo, run your new line down through the floor into the basement then bring it back up into the other room. ( You can run 4 lines off of the 3x4 switch with only the two lines coming in, so you could run one tivo and 2 standard; two tivos, or 4 standard off the one switch.) IF HOWEVER, you have dish with 3 "eye's" on it, you DO NOT need to add a switch as one is already built into the LNB assembly on the dish itself, you'd have to run any extra lines from that.
To the second part of your question:
If you are planning to upgrade to a total of 2 HD DVR units eventually, (note they will NOT be TiVo branded units. DirecTv and TiVo no longer partner and the HD DVR are now built in-house by DirecTv) the dish that will be installed with the HD has a multiswitch incorporated into the LNB assembly that can run 4 separate lines off of it without a secondary switch needed. So if you get two HD DVR's 2 lines each you'll have 4 total lines coming off the dish, 2 each to the DVR's.
As for the issue of digital/OTA, your satellite signal is already digital. The 2009 transition won't affect you. If you watch TV with an antenna on an old analog TV however, you will need either a satellite box, or upgrade your TV to one that has a digital tuner built into it. Maximum distance to recieve the OTA without an amplifier is roughly 30-38 air miles.
Hope I've answered what you were looking for, once again welcome to the forums, there are a lot of very knowledgeable people here who will be happy to address questions you may have.