Brian - ZL3BCO - was kind enough to lend me a TNC to have a play with. I've connected it to my Mac using a USB-RS232 adapter and can control it either using my favorite terminal-emulation software package (ZTerm) or using a dedicated TNC controller package such as MacTNC.
So far all I've done is access the local digi frequency for monitoring purposes and started broadcasting my own "UI Packet" which isn't quite yet fully APRS-compliant. But it has been fun thus-far!
I also had to make up a cable to go between the TNC's I/O port and the FT-7800's data port.
I mainly wanted to learn more about packet radio and APRS before my new toy arrives which includes a built-in APRS tracker and GPS receiver. But more about that when it gets here...
** Update 17.10.09 - my 'new toy' (more on that later) is on backorder so I decided to finish getting my "UI String" correct and broadcasting from the FT-7800 via the TNC pictured above. I now have my lat/long coords correct and am succesfully showing up on aprs.fi web-site around the Nelson region. The UI string I'm beaconing every 20 minutes is currently as follows:
!4118.63S/17313.60E` Mac OS X 10.6 Snow-Leopard http://zl2fsk.mac.geek.nz/ /A=000250