How to 301 redirect several different domains to my main domain?

Hi

I have several domains pointing to my forum and I would like them all to be 301 redirected to my main domain so that I don't get penalized for duplicate content. How do I do that via htaccess?

Or does google see that all domains run on the same ip and therefor does not count this as duplicate content?

StarBuG

Please check the following thread 301 Redirecting Domains

Thanks