Modifying the upload form

I am actually using WPMU 2.8.6 but i figure that the upload code is the same or at least similar in theory.

I created a plugin where users can create photo albums and link images uploaded via the build in flash media uploader. I am however looking for a simple and effective way to add some script, action or filter so i can automatically insert the uploaded images to a certain album (f.x. media-new.php?album_id=12). In an earlier WP version i managed to add a mod to make this happen but do to a recent hard drive crash i lost the code i added and now i can’t find the right way to do this anymore.

Has anyone a good solution to my problem? Is there maybe a way i can use actions of filters to make this happen? Basically what i need to get the $attachment_id/$post_id on each file so i can link it to a certain album.

Merry christmas ??