using something other than computer modern

[Tony Dancer]

Dear all,

I understand that in Layout/Document I can change the font my document
uses. But what i need help with is this - where does Lyx get this list
of fonts from, and how can I add fonts to it? 

And, in addition, how would I select an alternate font that is not
computer modern using tex-mode? (say, to be my default Roman Font)

Thanks for your help

Tony