I have searched around for this, and have tried multiple approaches. I have enabled and disabled, installed, removed and reinstalled modules, but I can't get this to work. I'm probably missing something minor, so I'm going to try the community option now.
Currently I have the following (relevant) modules installed: GeSHi field, GeSHi filter, GeSHi node, WYSIWYG, IMCE Wysiwyg API bridge, Wysiwyg, CKEditor. All of them are in site/all/modules, except for CKEditor, which only worked with wysiwyg if I put it inside libraries.
When I go to Administer > Site configuration > GeSHi Filter, it says the library is installed and all seems to be looking fine.
When I go to Administer > Site configuration > Wysiwyg, it says that CKEditor is installed and when opening "filtered HTML" (or full html or php code), I can see and enable the buttons: IMCE, Geshi-code, Geshi-php, Geshi-bas, Geshi-html and Geshi-css. I have all these enabled!
However, when I go to Content management > create content > blog entry (or something else), I can't see buttons for php, code, html or css. I don't see an IMCE button either, but it is working when I click the image button, so that's fine.
I've also tried Disabling rich-text and typing code or php-code, but neither are displayed in the blog entry when I submit it. Anyone out there that experienced similar problems and that can help me?
I'll be happy to answer more questions about this!