KDE3, in my experience, handles fonts very well. Much better than the Win XP I use at work.
Maybe try running your application from the terminal. Any errors reported?
Otherwise, if you have disk space, install KDE (you don't have to use it, but the necessary libraries will probably be installed). Disk space is cheap now.
If you'd like a just "install some application" solution, I cannot help you, because I do not know enough about your installation, or the interaction between gnome and KDE3.
Let's face it: "Ugly fonts" do not detract from "functionality".
If it works, I'll use it, even if it is "ugly".
Maybe the developers will get around to fixing it, maybe not. xvidtune is an example: It is very ugly, but I rarely have to use it now. If I do need to use it, I can forgive the "ugly" font because it does what I want it to do.
The bottom line is that you are mixing compiled-for-Gtk applications with compiled-for-Qt applications.
This usually works for functionality, but not always for prettiness.
Choose what works for you.