Custom file types question

I'm trying to figure out exactly how much work would be required to modify Gallery so that modules can add support for additional file types (like .avi). I've made the necessary changes to my test gallery so that I can add .avi files using the Server Add module and created an additional module to handle displaying the file (which as of right now just displays a download link). The problem I'm running into is that the link in the album doesn't work (it loads an empty page with no error log generated). If I manually type in the permanent url (/gallery3/index.php/video_avis/15) everything loads fine. I'm guessing there's still a file or two in Gallery I need to modify to make this work, although I haven't been able to locate the right one. Anyone know what the file(s) I need to modify to make this work right are?