autothumbnailing with php and mcpuk

I've installed FCKeditor, everything works great.. set up the mcpuk file browser, and the thumbnails display fine for me, despite the errors some people are reporting.

Here's what I want to do: when an image is uploaded, I want it to return a thumbnail image that links to the original in a pop-up window, instead of returning the full-size image...

There's so many files in this program, I don't even know where to begin! Could someone at the very least point me in the right direction???

Thanks!