Cannot load GFX.WAD in Quake.

Error: W-Loadwadfile: couldn't load gfx.wad

I found out why this happens - it happens if your directory structure is not right. Note that you won't find the gfx.wad file because it doesn't actually exist as an ordinary file - it is part of the PAK file.

Make a subdirectory in your Quake directory called ID1 and move your *.pak file, *.cfg and *.sav files into that folder.

That should fix your problem.

Also, if you have trouble using TCP/IP with a message about SIGSEGV and a stack fault, there is a possible solution here.