From the horses mouth, the official specification:
http://www.ofcom.org.uk/static/archi...df/mpt1327.pdf
An easier to read initial guide:
http://www.radio-electronics.com/inf...ingsummary.php
Free Windows-based software for tracking MPT1327 systems with a logical channel plan:
http://www.linato.net/trunkview/
(this site is in English contrary to the note I've just seen on the "wiki" trunking software page).
A more basic free decoder is available from:
http://hometown.aol.de/trunksniffer/index_2.htm
If the system uses a custom channel plan then software such as PTrunk, Ftrunk or Trunsniffer Pro are needed. These are not free and the first two use a hardware modem attached to your PC.
A guide to setting up the free software is at:
http://www.tarapippo.net/mpt1327/MPT1327.html
There are yahoo groups devoted to the various pieces of software