what does the .dat contain? :s
well basically a pk3 is a winzip v6 compressed file

and the reason to pack a level is just to get all the files in a single place more than compress.
So try the level without packing to get the directory structure you need, then simply highlight all of them and then right-click > winzip as... (v8.1) and type [name].pk3 and i'd recommend only using normal compression, it can work at higher compression levels but also becomes unstable on some systems (still unsure why)
Ever uncompressed any of the Quakes to the Base directory?
Tell ya they load alot faster

But also take up almost twice the space - hehee
"For the Greater Good"...
Kyi'Aun (Jedi Master) Rai'Ka