Tom,
Why aren't you using the content repository. It already handles most of the features you need. It also handles storage a little more easily, allowing file system or database storage of the actual media.
Mark,
There is a movement to simplify the existing attachments package to do what you are suggesting. It's on my list as part of clearning up general comments.
So, in all, storing media in the content repository and using the existing cr_item_rels table to relate the media to an object seems the best way to go.
I definitely want to see this type of solution for future CMS work.
