Well, I didn't read the terms of use for fileplanet, but I wouldn't be surprised if the registration opted you in to receive targeted spam. But you shouldn't let that dissuade you; if you've been using the web for any reasonable length of time you ought to already have an email address just for the purposes of signing up for stuff...
http://www.gamesas.com/index.php?app=forums&module=forums§ion=findpost&pid=2675609
See this is one of the discussion I get so tired of: the "I don't want register, just because" one.
IF you are hesitating to register (not only referring to you juv3nal) try indeed with an alternate e-mail address. But this isn't necessary at all - in over two years of registration at Fileplanet with my main address I have yet to receive the first spam message.
Another ridiculous thing I read here over the last few days was no registering because Gamespy "is known to distribute spyware". I'm not even going to discuss that - I think it's clear that when you don't download any of their Gamespy Arcade software or so, but just register to their website, you cannot even get spyware.