Tree widget with multiple selections

[Samuel <sciyoshi gmail com>]

Hi, I was wondering if there was already a GTK widget that's like the one
people use in installers... (I don't know exactly how to explain it, but
there's a list of features in a tree format, and if you select everything
under a node, that nodes checked too, but if only part are selected, then
the node is gray... If anybody's used amaroK, its the same as their library
selection window.) Does one exist already or do I have to write it from
scratch? Thanks :-)
ps. that wasn't very clear, so I can clarify if anyone wants