Open source Tool/Script for visual editing of xml

Question

In one of the propitiatory product on which I am working needs configuration to be setup using large XML files. So I am looking for a solution to easily edit the XML is a visual interface. Tried following

1. Visual Editor for XML VEX Eclipse Plugin (very early, so features missing)
2. Using XSLT (Ruled out, Considering the size of DTD's)

Any other tool (similar to vex), which will let me define my own stylesheets for XML Files and/or looking for a different approach.