WordPress MU

I'm expanding Wordpress to function more like a CMS. This includes relating image to a post.

Currently I have a text field where I paste an image path. Now I want to click a button which opens a dialog box, then I navigate to the right folder and select a file to "open" (from server side).

The file path is returned.

How can I go about accomplishing this?

I've looked at media.php to see if I can use the part which Wordpress already uses. But I can't figure out which part I should use.

Any help appreciated.

You can do this with Wordpress's built in Post Thumbnail feature. You can read up on how easy it is to implement here: http://wpengineer.com/about-wordpress-post-thumbnail/

Although you would need to upgrade to the current version of WordPress to keep it easy.

Yeah, I just discovered this this morning actually.
This really should have been there as default.

There are a few things missing though:

1. You can't see what files is selected
2. It's placed in the sidebar
3. How would I go about if I want one small picture in article listing, but another in full article?

3. How would I go about if I want one small picture in article listing, but another in full article?

You need a theme that shows the thumbnails on the front page. Less about usage, more about using the proper theme.