Bouncing spam rarely does any good. First of all, <i>if</i> the domain and e-mail address is valid and not temporary, then it's likely that it's some innocent guy's address. Spammers nowadays send from some random guy's address. This has caused a lot of innocent people a lot of frustration.
The best solution is to setup <a href="http://www.spamassassin.org/">SpamAssassin</a> and configure it correctly. This would be if you used Linux. I do not believe it's been setup to work with Windows. If you run Windows, perhaps see if your ISP would setup spamassassin for your account specifically, though it may not catch all e-mail.
But back to the original point, you do more harm than good with bouncing. I wouldn't recommend pursuing it at all.