Building GAIM for OSX Panther
The hard & geeky way. You will need to make sure you have these packages installed first. pkgconfig, glib, gtk, atk, pango, gettext, fontconfig, expat, xft2, XFree86, freetype, and GAIM. If you get errors building these you will have to refer to the developer site. There is time involved in this, so, only applies to you geeks out there that have built software from source.
The easyier way. Here you can just download FINK, FINK Commander, and GAIM. Install.