[XeTeX] Adding font features to LM fonts

[Till Rettig]

Hi,

I was wondering how I can influence the font features of the LM family 
that is the default in xetex/fontspec. I tried it with the 
\normalfontfeatures{} but it complaines that there is no font
selected so far. I tried also to install the LM fonts in my font 
directory but it seems they are not really named as a family so I would 
have to state each font explicitly for all type faces.
The background is that I would like to use the old style numbers feature 
with LM -- but so far I couldn't figure out how to.

Greetings
Till