A good Nokia service center should look up the phones IMEI in their database, and see the production date, and therefore see if it's still under warranty. Some countries in europe grant you a 2-year warranty on a Nokia. (At least the Netherlands.) If still under warranty, they will probably have it fixed (or even better replaced with another model).

This way is not always the most convenient for your warranty length, for your N900 could have laid in a store for months before purchasing. So the factory warranty could be shorter than the official, but worth a try.

Also, remove everything from it before having it repaired (back cover, battery, stylus, microSD). And backup everything first.