How to change the File upload dialog

I've written a file browser and have it integrated with CK. Lovely job guys, easy to do

I've got upload functionality in the file browser that uses ajax to upload the files, creates thumbnails, converts video and audio to flv and mp3 and all works well. The problem I have is that I can't figure out how to change the upload tab on the CK side of things.

I need to pass parameters from the upload tab to the upload script (thumbsize, audio bit rate etc). How would I go about replacing the upload tab with my own or change it behaviour?

EDIT: think I've found it