icon = .\mxoicon3.ico
That's all... there is an icon called "mxoicon3" as well. Both claim they were last modified in Feb 2006, if that helps at all.
I just realised it's not showing an extension, I must've hallucinated the .inf extension. Most of my files don't have extensions, and I have a vague memory of some setting to hide common file types, so I won't worry about it!