Can a key from a donor vehicle be recoded to another ? If so what is required ?

The chips are supposed to be a "one time only" programming, you need to have the immob pin code ( dealer or VagTacho) then with the pin use VCDS to program the chip in the ignition or you can buy a separate chip programming tool that is just a read coil connected to the USB lead

Is vagtacho through the odb port ? Then use vcds again through odb port to code key ?

Yeah all done via the OBD connector, or I have another lead that you can code a key away from the car

Cool. What is the other lead called ? Where's best to buy from ?

This is the lead I bought http://www.ebay.co.uk/itm/291917693587?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT & this http://www.ebay.co.uk/itm/162272355801?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT  & the immob transponder chip http://www.ebay.co.uk/itm/252605444892?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

So is it pretty straightforward ? Is s new transponder chip required ?

The chip can only be "written" once, so if your going to get a key from another vehicle you will need to replace the chip with a virgin one, then "write" the code from your immob into it either via the ignition switch reader coil or with that unit I linked to

Are both pieces of software required or wil VagTacho do it ?

You need the Vagtacho/commander  to get the immob pin code from the speedo, you then need VCDS or that stand alone set-up to code the chip 

The links show those as 2 separate items no or I'm confusing myself ?

Yes they are different items, I bought the basic one first, to get the pin code, then decided to buy the second one that could code a key away from the car

Ok I have VCDS, so VAGTACHO and a chip and I'm sorted ? Any soldering required for the chip ?

No it just clips into the key fob, you might need a bit of "Blu-tak" to stop it moving about,  there's a youtube link at the bottom of this http://wiki.ross-tech.com/wiki/index.php/Immobilizer_III_Immobilizer_Swapping_(Instrument_Cluster) that explains the procedure