Halo,
GPS units return a base value of Lattitude and Longitude as referenced to the WGS 84 ellipsoid (World Geodetic System 1984, a world wide approximation of the Earth's gravitational sphere).
So, a postition would be given as 09° 25' 34" N, 004° 34' 55" E, (in Degrees, Minutes & Seconds). That is Lattitude then Longitude (north then east), rather than East then North on a map.
To get the position as you have on a map, the WGS 84 position is converted to the local reference,(if needed) then projected on to the flat. That is, to go from an ellipsoid the size of the Earth, to an ellipsoid that best fits where you are, then flattened with the minimum distortion.
For Example WGS 84 converted to Airy Ellipsoid, then projected using OSGB 36 (Ordnance Survey Great Britian 1936) to give Eastings and Northings, the British National Grid.
Another is WGS 84 converrted to ED 50 (European Datum 1950), then projected on UTM Zone 32 V (Universal Transverse Mercator) for work in the North Sea.
Or simply, WGS 84 projected on UTM Zone 38 S. This would be an overlaid grid on existing local maps.
Your GPS unit has to be able to convert to the system your country is using. On the yellow Etrex, it is under Setup Units, for example.
Jed