This may seem like a trivial issue to some, but for years I've been a little puzzled at how to effectively plot GPS data onto the local (pretty darn good) topographic maps. See the problem is that the maps are made according to Costa Rica Lambert North (and South, but I live and spend most of my time in the "north" part). Thus the maps will have data points that are measured like 320030 253712 (which is somewhere near my office) but the GPS was spitting out coordinates in standard Degrees, hours, minutes...
so it was very difficult to use the GPS and the map together.
Fortunately for me, a client of mine spoke to an engineer and got started down the path to solving the problem. With the information he provided, I got online (boy Google is handy) and found a text in Spanish that specifically addresses configuring a Garmin GPS to read Lambert North.
On my eMap it is done as follows:
1) push "menu" twice
2) select "Setup"
3) push left twice
4) on the Advanced tab, go to Location Format and select "User UTM Grid"
5) enter Longitude Origin W84* 40.000', scale 0.99996, False Easting 499800m, False Northing -885244m
6)hit save
7)scroll down to Map Datum and choose "NAD27 Central"

There, you're done. It's just that simple. Hope this helps some of you out there, I think it'll help me quite a bit both with having fun and work.