1) no gigabit (likely no 100 megabit due to crosstalk)
2) no standards

a $13 switch solves the second problem. http://www.newegg.com/Product/Product.aspx?Item=N82E16833166034
a $22 switch solves the first problem. http://www.newegg.com/Product/Product.aspx?Item=N82E16833704042

I tried to remain child-like, all I acheived was childish.

Think you may want to consider using something like this?

CAT5e Economiser/Doubler
Attach two PCs to one CAT5e cable

    10-/100-Mbps operation.
    Splits one 4-pair CAT5e cable into two separate ports.
    Housing can attach to wall.
    Use in pairs.

http://www.blackbox.co.uk/prod/fau962/1/7/1/Copper-Connectors/Connectors-Adapters/Cabling/

But you should really think about putting in extra cat5 points.

Like Jimbo says, a small switch at the location is a better solution than violating standards and making a mess of things...

interesting.. our scenario was that we needed four dect analogue telephones to the outdoor area, issue was that there was only one cat5 cable already there.. the requirement for the computer was not relevent anymore, so the cat5 cable was redundant..

as the requirement changed so now they wanted 4 dect phones instead.. quickest option i found was that i could split the cat5 into 4 pairs, crimp those into pins 4 and 5 on the telephone end, and then the same on the other comms cabinet end.. and voila, i have one cat5 cable carrying 4 telephones.. works a treat, no issues for the past 6 months or so at least since they have been installed.  

Many Thanks
Yurov Ardyy

But you are not sending data over those wires, just voice.

I tried to remain child-like, all I acheived was childish.

Sorry, i should have mentioned that.. but yes, its just voice, no data..  

Many Thanks
Yurov Ardyy

I would terminate all 8 conductors onto a keystone jack and use a splitter to break out the pairs. I'm don't know what is available in the UK, but local electronics stores might have some suggestions.

I "FEATURE 00"

From my experience when having to be forced to se this method I have never encounter any cross talk.  Speeds
are just fine for general browsing and UP/Down Loading.

if its just voice its no different than using a 4 pair cat3 , use as whatever pairs you need punch it down any way need  

So far for normal everyday use on these PC's I have not had any complaints from the users. I think there is enough horsepower for them for emails, browsing and low volume DL.

Firefoxfire
The old timers & gurus in this group know it would work but are also smart enough to not say anything or try and talk you out of it. If (when) there is a problem later, it always seems to come back to the exception.
Example
Auto-lube company wanted remote computer and only had 1 cable installed due to cost. They split cable when they wanted additional phone and printer. We were called in to diagnose chronic intermittent problems (we didn't do the initial). We discovered electrical ground was improperly installed and determined printer was using data cable due to ground float. We asked if they had computer problems and they reluctantly disclosed they were going through A-D cards like hotcakes but attributed it to a stupid supplier. After proper install with proper cables they never had a problem. In fact I even got a 10% coupon for an oil change.
You are the vendor, when the customer is too cheap to do it right, it will usually bites you.
Cheers

Regards
Peter Buitenhek
Director
BidQwik.com
ProfitDeveloper.com

"Never settle for a job well done...always look for cost cutting measures"

To do this sucessfully you don't split the pares thats a no no. You separate the channels. Since 10/100Base-T only uses two pares it is possible to do this! I have done it myself many times with out a problem and you still plug in a standard patch cord. Best advice you can get is hire a Certified Installer and don't let your computer programmer touch the wire it does appear like they are the ones who make a big mesh out of simple cabling jobs...