Font Face problem

Hello,

I have a problem with a special font that I use on my website. I've been messing around for hours, but can't find a solution.

You can see my problem clearly on this page:
http://www.conversal.be/webdesign/over-ons

In Windows 7 - Firefox, it's (on some computers), the h2 titles are displayed like this:
http://www.conversal.be/bold.png

In IE & Google (on the same computer as above) it's displayed like this:
http://www.conversal.be/notbold.png

On my laptop (Windows7 too) it's displayed correctly in Firefox correctly too!

The problem is not only on my computer, because i've seen it on other pc's too.

Now, does anyone know a solution to this problem? As you can see, the bold version is really ugly...

Thanks in advance!