HTPC, DSL and CAT5 wiring question

Here's my situation. I'm renting a home that has CAT5 wiring. This can be used both as a phone line and a Ethernet line.

This outlet on the wall is paired with a cable coaxial plug. Seems like the general idea or assumption was that the user would use cable as the internet provider, and that using a router, the user can plug back in a ethernet cable right below it to the CAT5 plug.

However, I use DSL. I want to take advantage of the CAT5 wiring, so that I can use that to plug into my HTPC downstairs - the wireless G isn't quite cutting it,and I want to see if I can save myself from buying a wireless N, since the ethernet cable is faster anyways. There is too much lag playing anything from my desktop upstairs into the HTPC downstairs.

So I've got my router setup upstairs, and since obviously DSL gets its internet feed from the phone jack, which the CAT5 also serves as, I need to use that plug as the phone jack. This means that I cant plug in the ethernet cable coming out of the router back in to get connection with the HTPC downstairs.

Anyone have any creative idea on how I can accomplish this?

Thank you.