Hi WP1,
sorry for answering late. I have been very busy the last days.
I have followed the discussions on the web concerning FIR, sFIR and many other similar methods. All have their pros and cons, but none is perfect. A collection you can find on css-discuss ImageReplacement.
I had made some extensive efforts in a project to find a way to make it possible for a client to use his corporate font with Microsoft PowerPoint. I was sure there is a way if I only look and ask long enough. I was not successful because there is no way - either the solution didn't work technically or it was illegal or the employees could not handle the technique.
Since that time I am very careful with non standard techniques and these image replacements are more or less tricks - very interesting tricks indeed.
I would like to suggest that you think about going the secure way. First build your Moodle site with standards. When you have it running you could start to use the newest and best tested of these image replacement techniques to make your site "better looking".
I hope I could help you.
Urs