I don't think you can get a discount on trains. Here are afew websites with railpass info:

<a href="http://www.raileurope.com/us/" target="_blank">http://www.raileurope.com/us/</A>
<a href="http://www.ricksteves.com/rail/howrailworks.htm" target="_blank">http://www.ricksteves.com/rail/howrailworks.htm</A>

Don't forget that Eurail is not accepted in the UK; you'll need a Britrail pass.