"Scalable Vector Graphics" is a XML-based vectorformat.

I chose this one so you can zoom into the graph. Currently the best viewer is avaiable from Adobe:
http://www.adobe.com/svg/viewer/install/main.html

But it's still not very comfortable. Some hints:
Ctrl pressed               = zoom in
Ctrl+Shift pressed     = zoom out

or just rightclick at the graphics.

Here's a page about which programs use SVG, with some converters etc.:
http://www.w3.org/Graphics/SVG/SVG-Implementations