Slackware does not check for dependencies during installation. Given the name of the file/library that is missing however, it is trivial to determine what you need to install. Without the name, well, that is another problem. It wouldn't be libgtkspell.so.0 that you are missing, would it? That is Question #2 on the FAQ found through the gaim home page ( http://gaim.sourceforge.net/faq.php
I have not found it makes a bit of difference where I install the packages from. I usually cp the desired packages to a directory within temp so I only get the choice of the packages I want.