FileMaker Instant Web Publishing blocked - is it my firewall?

My FileMaker Instant Web Publishing database isn't visible to outside computers (they get the standard page cannot be displayed error message). My guess is it's a firewall issue, but I'm not sure.

I have two Windows XP Home computers hooked to the internet via a router & DSL modem. When I visit the website linked to the database on either of them, I can open the database without any trouble, but when I ask someone outside, although they can get to the website, clicking on the database link doesn't even take them to FileMaker's Database Homepage.

I have a third computer I'm not using - should I put the database (and only the database) on that one without any firewall, or is there some better way to do it without jeopardizing the security of the two I'm using? Thanks.
 
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