Hi pmolik,
I'm not sure anymore, if Geshi is the best approach for syntax highlighting, as it works on the server, so it needs server-side ressources to do the syntax highlighting, but even worse, it will considerably increase the (X)HTML that's sent to the client.
There are some JS based syntax highlighters available, which shift the work to the client, most notably
Alex Gorbatchev's SyntaxHighlighter (and recently I found
gcp). But the problem with the special (X)HTML characters ('&', '<', '>') remains. I had found plugins for tinyMCE resp. CKEditor, which should make it possible to insert source code usable for the SyntaxHighlighter, but both plugins didn't really work good.
A simple solution would be to add the code snippets not directly on the page, but instead in a special admin part of the plugin -- but that's quite cumbersome for many small code snippets.
So I still don't know, how to handle the syntax highlighting issue. I'll have to further investigate -- but that may take some time.

Christoph