Moving from Wordpress to MU- where is the wp-content directory for each blog?

I'm moving four Wordpress sites into one MU. I've read up on how to move the database by replacing wp with wp_1 etc. but what about the files that were in the wp-content directory like my images etc. If a blog has an ID1 in MU, where do I move the files from wp-content of the original Wordpress directory.

Thanks