Hi Peter,
I suspect it's due to the encoding of the XML file in question...in this case possibly being ANSI encoded This is not the fault of the webbrowser control per se. If you open the same file in any web browser it will likely do the same thing.
I don't believe there is anything you can do by way of changing properties of the control or calling a function on the control in order for it to show up properly.
A couple of options come to mind:
1) make sure the XML file is saved as UTF-8 encoded and if that's not possible then
2) At the beginning of the XML file you should see something like <?xml version="1.0"?>. Change it so it looks like the following: <?xml version="1.0" encoding="iso-8859-1"?>. It should then open up in the webbrowser control (and any web browser) just fine. Hopefully you could make this change in advance, wherever the file is being created, but if not you could programmatically add it to the beginning of the file as well.
HTH.
Regards,
Mark