Hi Paul!

I hat the display of any pop-ups en toolbars when reading the forum, so I removed most of the Alt="blabla" an title="blabla".

I guess you are talking about a "tooltip" which becomes visible if hovering with the mouse-pointer above an object? That's not a pop-up!
In (X)HTML 1.0 Strict the alt-attribute is required for the image-tag (if you remove it, the page will not be valid any more). If you don't like it, replace the content with an empty string (alt=""). But it's not a good idea anyhow. Users with text-based browsers - or if graphics are switched off - are left out in the rain.

The title-attribute for any tag is optional. Old IE's (prior to v7) erroneously show the content of the alt-attribute if no title-attribute is given. If you want to get rid of it, either remove it completely or (better!) set it to title="".

Let's look at an example:
The Ajax-preview is marked with a small "speech bubble" and the tooltip "Show preview" (that's the title). Without graphics you see the text "[…]" instead (that's the content of the alt-attribute of this image), and the same tooltip. If you remove the title, you see the content of the alt-attribute in the tooltip in IE<6, any nothing in modern browsers (might be confusing, because users have to guess, what "[…]" means). If you remove both the alt and the title, the Ajax-preview is not accessible any more!

Information from the W3C-specification:
alt-attribute: Text contained within the alt attribute is used to specify alternative information that should be shown if an image is inaccessible.
title-attribute: Text contained within the title attribute is used to display additional information.

That's exactly what the forum's scripts do (click here to check); you made some modifications in your forum, which resulted in invalid HTML (check here).