Spammers spoofing my "from" addr

[Trevor Smith]

Off topic but you folks are more knowledgable about these things than anyone I 
know...

I occasionally get returned mail failure notices because some jackass spammer 
has sent out mass spam using SOMENAME at haligonian.com (which is my domain) as 
the "from" address. When he hits nonexistent "to" addresses, the bounces come 
to me.

I don't care about the bounces, but what would you knowledgable people do 
if/when someone was/is falsely using *your* identities to send spam?

Is there anything I *can* do? Am I ultimately going to be cut off from parts 
of the 'net because it *looks* like *I* am spamming? Surely this can't be the 
case or you could get anyone "banned" from certain servers just by spoofing 
their "from" address and breaking the rules. No?