Ok so you've gone out and bought a new GPS, put the batteries in and its telling you something. But nothing seems to match the topo map you have in your hand. Before you go any further check the following.

This is particularly important for us here in Australia, as most, if not all GPS units come out of the box ready to be used in the USA.

Click on the 12XL or Emap images for respective screen shots.

First off check that your datum is set correctly, i.e. it is the same as the map you are using. Most Aussie maps in use, use the Datum, Australian Geodetic 1966. For Garmin's this is abbreviated Astrln Geod '66. Out of the box the GPS is set to WGS84. 

For a 12XL you can change this by selecting the Menu screen, then Navigation (NAV SETUP) , arrow down to Map Datum:, hit enter and scroll through the choices until you get to Aus Geod '66, and hit enter. Other Garmin's/brands should have a similar options.

For an Etrex, you can change this by selecting the MENU screen, then SETUP , then select UNITS , then MAP DATUM, then scroll through the options until Aus Geod '6  is selected.

Now the numbers on the Position Page say something like S 38 50.444' E174 47.608 but your map says something like 538000 6912000. You need to change Position Format from hddd mm.mmm to UTM format. Again  for a 12XL you can change this by selecting the Nav Setup  screen , arrow down to Position Frmt:, hit enter and scroll through the choices until you get to UTM/UPS, and hit enter. While your there change Units: to Metric

Make sure the time offset is set to +10:00 (Eastern Australian non daylight savings) or +11:00 (Eastern Australian daylight savings). While this won't change any of the navigation/position information, it makes things like sunset and sunrise times correct.  Again  for a 12XL you can change this by selecting the System Setup screen , arrow down to Offset, hit enter and scroll through the each digit until you get +10:00 and hit enter.