I have one of those Garmin GPS devices (eTrex Vista to be precise) lying around. Ever since I switched to a Mac full-time I have been unable to make any use of it because the cable to connect the eTrex to a computer supports RS-232 only, which is not supported by most modern machines. Some time ago I bought a cheapo Serial-to-USB-adapter, but was unable to get the device working with that one.
Turns out that most adapters don’t implement the full range of RS-232 features as required by GPS devices. Who knew? Garmin itself sells known-to-work adapters, but they cost around 50 €, which I find a bit hefty for just hooking up a five-year old GPS device for occasionally playing with it. But there is a much cheaper solution available: The Gilsson Serial to USB DB9 Adapter is specifically made with Garmin GPS devices in mind and works like a charm on OS X. On top of that, I got mine from Germany-based Globetrotter for as little as 20 €. (The catalog price is $44.95 though, so your mileage may vary depending on where you live.)
On the software side I have so far only used gpsbabel, which works well if one is only interested in extracting tracks and waypoints as GPX files. (One can import them into other software like e.g. Google Earth.) Garmin offers a bunch of OS X software for their devices, too.
Your blog post was very useful, I wouldn’t have found the Gilsson adapter otherwise. Purchased mine from otrade.ch in Switzerland.
Hi again
How did you connect the eTrex witht he serial adapter? I had to install the open source driver here (http://osx-pl2303.sourceforge.net/) because the original drivers (from Prolific who makes the chip) didn’t work.