The MakeitOne MP3 Album Maker allows you to pack or join your MP3 files in a single file - whilst still allowing full playability (in any mp3 player), tag editing and unpacking. It supports SendTo, Drag n Drop and is the most efficient MP3 album maker/wrapper/joiner around. Version 3.04 has added user stored settings for Album Prefix and Suffix, corrected tab order of textboxes and fixed a couple of bugs.
Also I think the caption on download.com is misleading: Edit tag, pack, and unpack your MP3 files. Makes it sound primarily for tag editing, whereas primarily its for packing mp3 tracks into an album that can be unpacked later.