Good answer is here:
http://maemo.org/development/documen..._2_2_tutorial/
And from compability page: "Installation packages created for Nokia 770 will work with Nokia N800. Single click installations will however need separate installation files (or .install files).
Most of the applications developed for Nokia 770 using maemo 2.2 will work as such with Nokia N800. In some exceptional cases porting from maemo 2.2 to maemo 3.x will be required, but it is typically simple."