drawing on top of maps

[John Carlson]

I was able to create maps and draw on top of them using
mapscript, but now I am wondering how to incorporate
this functionality into mapserv (a web page).  Is there some hook into
mapserver that I can define my own mapscript program to generate
the gif file?  This seems like a very easy thing to hook into
the template file (have a path to a mapscript program instead
[img]????).  Has anyone done this? I'm using 3.3.009

Thanks,
John Carlson