[nix]

Auto-detect the Attachment Type - Set this to yes.

Use AnyMedia BBCode when upload an attachment - Set this to yes.

Then look on the left hand side of your admincp. You'll see attachments. Look for

Attachment Storage Type. Create a folder in your forum directory and put the path in there. Select move from database to file system.

Make sure you do the template edit.

Then you just make a normal post and attach the media like you normaly do with other attachments. You don't need to do anything with the M button.