Preserve Code Formatting

hello

I wand to show little parts of code like css and xhtml in my post.
Now i use images for this see here http://reality-escape.net/blog/2007/12/26/how-to-make-a-image-navigation-2/

I have used this plugin (Preserve Code Formatting)
it works only i have this probleme.
When i insert the code between the <code></code> tags
wordpress removes the close tag </code>
and ad tru the post alot of new <code> </code> tags on different places.

I don’t understand wy wordpress made his own tags.

Thank you for your time
Danielle