UPDATE:
ok, after a few hours of reading to get caught up on zdoom, since i didn't know anything about how textures work or anything like that (and i didn't even know what hirestex was), i have reached a conclusion.
apparently, there is something wrong with the hirestex in the pk3.
please correct me if i'm wrong, cuz this is how i understand it, but zdoom (& hence st/gzdoom) require the actual images (whether they're textures or flats or whatever) to be in a /graphics/ directory. well, in the pk3 there is no graphics folder, so i extracted the contents, created a /graphics/ directory, cut & pasted the flats & textures directories into the /graphics/ directory.
then i compressed the files in zip format and renamed the filename & extension exactly how the original was named. (i also renamed the original file so as to not overwrite it).
BUT IT STILL DOESN'T WORK!

i need some help here if someone doesn't mind...
UPDATE #2:
i found some more info over on the zdoom forums. apparently, the reason it doesn't work is cuz of the zdoom devs! (ppl confirmed it doesn't work on zdoom final or svn, as well as st). here is a short "transcript" of the discussion about this pack not working:
HotWax:
I was able to get this to work by doing the following:
1) Extract the entire PK3 to a folder, ignoring subdirectories. When prompted, select to overwrite all files. This eliminates duplicate files in different folders (there are several files where there are versions in both the "doom1" and "doom2" folders.
2) Re-zip all the files back into a pk3.
3) Play.
Granted, this isn't an official fix as I'm sure there's a reason there are duplicate textures, and the skies are messed up by this as well, however it's better than not being able to run it at all.
I personally think the problem is in the way you're trying to handle Doom 1 vs Doom 2 with a single pk3. I think the only way it's going to work in ZDoom is to have a separate version for each game.
KuriKai:
One pack is the best way to handle it. Having seperate packs is a waste of space, bandwidth and it is confusing if they are in separate packs.
There was discusion about it here http://forum.zdoom.org/potato.php?t=14527 with a simple and easy fix for the devs of zdoom to do. but they seem to have ignored it
i read the aforementioned thread above, but apparently, as it stands, this DOES NOT work for zdoom or its derivatives! cuz of the way its packaged. its seems kinda stupid to me to release a package with zdoom in the filename when it doesn't work with zdoom!
one could get this to work by repackaging it the correct way, since the zdoom devs won't support this other way of packaging, but it was unclear to me as to how to repackage this and hence get it to work on zdoom/gzdoom/st...
