Take a look at:
http://www.icann.org/udrp/

Honestly, this is your best approach to getting 
the domain back, and you should be pleased to 
know that most resolutions seem to side in favor 
of businesses (some even accuse them of being 
biased towards businesses).

However, now that I'm looking more closely at 
some of the dispute-resolution providers, it 
looks like it would be about $1000-2000 to file a 
claim.  It's possibly, though, that you might be 
able to recoup some of that cost through legal 
proceedings if you decide to do so.