That sounds like great fun, I'd be really interested in a write-up of your project if you have the time. Particularly hacking the TV dongles, and working out the interesting GPS math!
rtlsdr[1] is the name of the project that lets you use your $10 USB TV tuner as a software defined radio receiver (bless those osmocom people). rtl-sdr.com[2] has some more information.
dump1090[3] is the particular project for decoding ADS-B broadcasts.
With £15 of equipment (USB Tuner and some TV coax hacked into an antenna) I'm looking at aircraft 200+nm away [4] (though today's weather doesn't help).
