Okay, I've got something I want you to try Jezza. Its a pk3 I got from PlanetQuake. Its pretty recent, it carries all of its textures in the pk3 in the proper format. It contains exactly one map, and its a really well done Quake III Arena map, with hardware lights, and some really outstanding artwork that the map maker did. It is called nightgallery, and it looks alot like a gallery. There is one texture that seems to be missing, but that serves to show you what that does to the map in GDK/DBPro. Its the roof of the upper level, and I think its probably a skybox, so that is easily fixed in DBPro. Skyboxes are entities, and there is some functionality missing in GDK/DBPro with respect to the entities.
I downloaded several recent pk3 maps from there, but most of them are built for QIII and mods, so they usually rely on those textures. If your map isn't loading, or your display just looks black, that is why in most cases.
If you open this file using WinZip, or any other zipfile utility, it will show you how a pk3 should look. Notice that the map is in the root directory. There is a directory called textures. That is where all of the textures are for this map. The bsp file gets built with that dependency in it...the texture paths. As you already know, they cannot be .WAL, or .PCX, or .STL so avoid those types whenever you can when using bsps in GDK/DBPro.
Here is a DBPro app that will load that map and you can push the camera around to see this guy's awesome artwork. I imagine that you could get the same thing using GDK.
REM Project: loadfrompk3
REM Created: 4/3/2008 2:03:10 AM
REM
REM ***** Main Source File *****
REM
load bsp "nightgallery.pk3", "nightgallery.bsp"
set bsp camera 0
set bsp camera collision 1, 0, 0.65, 0
set bsp collision threshhold 1, 0.001
do
control camera using arrowkeys 0, 0.1, 1
position camera camera position x(),camera position y()-0.01,camera position z()
sync
loop
delete bsp
end
...and also be aware that you get "spawned" at 0.0, 0.0, 0.0 by default, and that is not always a valid place in a bsp, so you might just fall into oblivion sometimes.