Just a follow-up: I didn't get it to work but it wasn't that bad of a problem, I just stopped using the pop-up window and made every one of those links a new page.
I still tried to get it working though but didn't find what was wrong with it. I tried using Virtual Box to test it on IE6 and it worked (XP SP2 with the latest IE6 version). But on IE Tester it doesn't work at all.
