here's a screenshot -you have to click »additional options« like it was said before and then »choose file« (or what it is in english -the button next to »attach«) - a window will open where you can -well- choose a file to be uploaded.
![Wink](http://cal-look.no/lounge/Smileys/default/wink.gif)
you can use »
![](http://)
« if you have a path to some kind of file -then you'll have to copy the adresse in between.