dropline gnome is an i686 optimized gnome desktop build specially for slackware. it was originally developed by Todd Kulesza and now its community driven project.
the problem with dropline is that it intruds your slackware installation and replaces rather important packages like shadow + adds pam, which could lead to permissions problems, etc... and its difficult to remove dropline without messing the entire system(well... in my case ive removed it using rescue cd...) IMHO a desktop environment shouldn't go that far. perhaps you can install *only* gnome packages but im not sure if this will work.
anyway, try searching LQ slackware forum for dropline keyword as there were a number of topics. also
http://dropline.net/forums/ is a good place for research. and decide is dropline gnome really what you want(you need to be using 2.6 kernel btw).
and if you dont even use gnome and only need libs - install the official packages from your slackware cd2 or any mirror. im not aware that any app actually requires 2.8x gnome libs.