Creating a home Ethernet out of installed but unused Cat 5

["Bruno" <bruno.lerer@xxxxxxxxx>]

The phone company has installed, throughout the house, shielded Cat 5
cable with 4 sets of wires. One is used for phone service, while each
of the other three is terminated with what looks like a plastic sleeve
imprinted Dolphin (just in case it makes a difference...).

I have a wi-fi broadband router on the second floor (physically
connected to two computers); I also have another computer in the ground
floor den which is currently wirelessly networked with the others. The
phone company's breakout box is in the basement, naturally.

For various reasons, I would like to physically network the first floor
computer.  Ideally, I would like to install in the router room a wall
plate with an RJ45 jack, with a patch cord connecting to the router.
Currently, the Cat 5 terminates in a standard RJ11 jack.  The same
would go for the ground floor den; there, however, the Cat 5 terminates
in a wall plate with a coax F-type jack at the top and a standard RJ11
at the bottom.

So that's the question - how do I approach a project like this? In
particular, how do I go about making sure that, while I go two floors
down and then one floor up, I am still connecting  the same set of
wires to the appropriate terminals in the router room, the breakout box
and the den? What type of tools would I need to accomplish this?

Thanks.