If you are tired of adding new repository's one by one in application manager of Nokia 770/800 follow these instructions for replacing repository list.
Repository list in Internet Tablet-using Linux Advanced Package Tool features with Nokia 770-800
I generated a list of repository's that I know and uploaded it. I believe that instructions are as simple as possible.
This method was tested on Nokia 770. I'm not 100% sure that it would work for Nokia 800. I'll highly appreciate if somebody would be able to test this with Nokia 800.
If you know repository's that were not included, add them here or in comments to my article and I'll update this list.

I'm getting errors when I try to refresh the applications list.

www.gronmeyer.com/it/ has an easier answer.

Errors when you try to refresh often indicate a temppry problem caused by the repository makers. You can look at the log file on application manager for more info.

Disable repository's that give errors. You can start with disabling most of them, then add one by one and check.
The idea of compiling this list was to simplify process of entering majority of them without big efforts for typing and searching for the address. Not all of them would work.