Having got started with APRS, I have implemented a Rx-only iGate  using an Asus eeePC  with a RTL-SDR dongle and direwolf software.  This was done initially with a Raspberry Pi using the project detailed by G6NHU, but extended to use the latest versions of software.

This is currently on APRS-IS as M0RNW-10.

It is envisaged that this will become a two-way iGate/digipeater with the use of a Baofeng transceiver, together with a arduino based weather station (in development).