[NTLUG:Discuss] OT: sharing/splitting a Cat5 cable

[Jack-I-Need-a-Job-Snodgrass]

I have a 100 foot run of Cat5 cable. I REALLY, REALLY don't 
want to run a second 100 foot run of Cat5 cable. I'm still patching
the extra holes from the last time I did this. :(

For a home LAN, can I get away with splitting this cable run into 
two different LAN connections? I don't want a hub... I want 2
physical connections out of the one piece of Cat5 cable. One 
will be my cable modem ('public' side of my home LAN )  to my 
linux box and the other will be the 'private' side of my home LAN.
I could have the linux box next to where the cable modem is 
located, but that's not a good spot.

Now if I can split the cable and run with this setup, what's the 
most cost effective way to do so?  I don't really want to spend 
$100 to do this. Are there any simple / cheap devices that 
will let me use pair 1 and pair 3 of a Cat5 cable at the same 
time? 

Thanks - jack