In reply to Gazlynn:
It should be possible to change the co-ordinate mode of your GPS... it'll be under settings, or units, or somesuch.
If the map you've got doesn't have a suitable grid system though, you're out of luck. Have a look at the blurb on it, and see if you can see any mention of something like 'UTM' or 'GPS'. Not all maps are guaranteed to have a GPS-friendly coordinate system, and even if they did it isn't guaranteed that a cheaper, older device like the Geko would understand them anyway.