Whole House DVR and Network Setup

I have the whole-houes HD-DVR (HD24) and a high def receiver in separate rooms.  Right now they "see" each other over the coax network with no problems. However, if I try to connect the internet to the HD24 upstairs (via an ethernet cable), the other receiver no longer connects into the HD-DVR.  It seems that as soon as I connect the HD-DVR to the internet, it assums all the other receivers are connected via my network and defaults to sharing that way.  Problem is, I can't connect the HD receiver via ethernet cable - it's about 100ft from my internet router.  I could connect it wirelessly, but I don't have a wireless adapter for it (plus, I don't know what type of wireless adapter to buy for it).  Is there a way to connect the HD-DVR to the internet AND keep the whole-house DVR service via coax?

Thanks!

By the way, I'm an Electrical Engineer - so if you can answer, get as technical as you want!