"Gernot Frisch" wrote
> Hi,
>
> I've upgraded my webspace, so it can handle php4 now. I must provide a
> forum for users. Do you know any good free source code for a web based
> forum in php?

Nice board is www.phpbb.com

>More, I have 1 MySQL database - what is MySQL, and what
> can I do with it other than with php?

www.mysql.com learn what Mysql is
www.php.net learn what php is

That's are basics, what is database, what is a programming language. Not the
right group to tell you the basics and concepts of databases and/or
programming language.

>
> Next, I want to provide a way for the user to enter a product link and
> a product cathegory, and then there should be a site, where you can
> sort all entered products and click on "detail view" for the product.
>
> More, is it possible to let the user upload an image (checking for the
> image's size to be smaller than 100kb) with the product description?
> Can I resize images with php to match 100x100 pixels?
>

Maybe you are looking for an free CMS like www.postnuke.com

Michael