Not sure about 3rd party repositories, but it should be set for OS2008 (Chinook) "by default". If you look at the application manager, and there are nothing set for the "distribution", then it will assume "Chinook".

(At least that how it seem to work for me, when there was occasionally problems with some of the Nokia Repositories in past weeks... in the error message "Chinook" was mentioned in the path. If I set the distribution to "Bora", then different set of applications pops up. Too bad almost none of the Bora apps installs due to missing libraries etc...)