Greg Utas offers this information about using a Garmin GPS in Argentina:
I took my Garmin 255W to Argentina and it worked great. Very useful for driving around the city of Salta. The maps were loaded onto a small memory card that goes into a slot on the side of the Garmin. I ordered a preloaded card from travelbygps.com.
You can download the maps yourself, but for $20 I didn't want to spend time on it. The maps also include Chile, Uruguay, and Paraguay.
Not everything went smoothly. My 12V (cigarette lighter) adapter would often fall out when driving over a bump. You can imagine the hassle, so I travelled around Salta in search of a new adapter. Marc Chagall, located at Florida 11 in the pedestrian mall area just south of the Hotel Alejandro I, had a 12V adapter with a USB port. They also had a USB cable to plug into this port, one with the right connector for the Garmin at the other end. This adapter could still fall out, but twisting a car key under the spring clips widened their grip to the point where they would hold.
The maps don't know about La Estancia's roads yet, apart from the southern service road. And a couple of times, they wanted to send me the wrong way down a one-way street. So pay attention.
On 2 April 2011, Jeremy commented: You can find Garmin-compatible maps of Argentina and Uruguay at www.proyectomapear.com.ar. It's free, by the way, and it works.
