Which version of the software?
You will need an unlock code to make the software work. If you registered the product with Garmin then you will find your code in the "My Garmin" section of their website.
If you don't have the unlock codes then you will need to buy another one.
Either way, contact Garmin. If you have the unlock code then they will probably send you another CD free of charge, for the edition of Mapsource you have rights to.
Incidentally, City Navigator 2008 is available for the 2620 now. You might want to consider taking advantage of the weak dollar and buying yourself an upgrade anyway.