Can you check what version of the maps you have? I am assuming that as you have a Garmin then it is Navteq maps on your machine. If you bought in October 07 you should have (at least) Navigator 9 maps installed.
Unfortunately, Garmin will shortly release v10 maps (Navigator 2008). I say unfortunately as you should not have registered your unit so quickly. Garmin give one free map update to owners on the basis that you bought your Sat Nav with the old maps installed. However to benefit from this, you should have waited until they released the new maps.
If you are driving over fields then I think the maps on your unit are much older, as v9 maps are very accurate and are really only missing the major construction projects of the past two years i.e. Fermoy bypass, new M4 road etc.