That error message says that it cannot find the correct version of the gtk library for gtk-gnutella.

Now, if you're using QT you might not have gtk of any version installed on your system, at which point I advise you install it, in Redhat based systems it'll be a rpm file to download, for debian its a .deb and for slackware you should be able to find a .tgz for it.

If you do have gtk (for use with gnome and other apps) it could just be that you only have gtk2+ rather then gtk1. when you compile gtk-gnutella specify the environment as gtk v2 rather then v1. Read the README file which comes with the source.

Otherwise you could always find a binary package for the system you're on (again, it'll be rpm, deb, or tgz depending on the flavour of linux) and as long as you have all the required components (rpm and deb files will tell you what components are needed, tgz files will just install but when it comes to running the program it won't work)

Hope that helps