So does that mean you installed gtk+-1.2.9 from source with ./configure, make, make install? The simple thing to do would have been to use the Mandrake package management tools to install libgtk-1.2-devel (that's not the exact name but I'm not rebooting just to look it up). Though now I come to think of it xmms should be on the Mandrake 10 CD's. It certainly was with Mandrake 9.1.
Anyway, I've wandered off topic. Try the Mandrake Control Centre, it should be possible to install what you need there. If that doesn't work you should be able to compile xmms from the source by setting these variables first.