Generally the red x's in IE mean that the URL pointed to (ie, where the picture is supposed to be) doesn't exist. That usually occurs because the person who posted the link (or if it was a link on another site, the site owner) moved or renamed the picture. (That's why we STRONGLY encourage members here to attach pictures... the names won't get changed and they won't get moved). Firefox, BTW, doesn't bother to display an X... it just leaves a blank space.

As jockeys said, it's also possible that you have security settings set in a manner that the "firewall" features embedded in IE and Vista are blocking the address. If you post a couple examples we can tell you whether the poster moved the pics or it's your settings.