There's the wiki page: http://wiki.maemo.org/Documentation/...ion_to_Maemo_5.

I guess the "main" problem in porting complex applications is that most of the UI needs to be redesigned (finger UIs, no hierarchical menus, etc).

Note that I have no experience in this, I dabbled a bit at "hildonizing" a Python Glade application in Diablo (N800/N810), which was relatively simple, but it has just about no relavance for Maemo5 aka Fremantle.

I guess you should start with telling in what language(s) you would like to work on.