Couldn't load pics/colormap.pcx: You are missing files. You need to install the maximum of the cdrom and the FULL 3.20 patch. Those are required, no getting around it.
SZ_GetSpace error: The Quake 2 config allows for a maximum size of 8kb. If you added to or created a config then take a look at the size. It can't be larger than 8kb. Break it up into smaller files and connect them by adding the line exec mynext.cfg or whatever you call it at the end of the previous config.
Cannot fall back to software refresh: This means that you have two copies Quake 2 running. Somehow you accidentally executed the game twice. Need to shut one down.
autoexec.cfg didn't start: Most likely you saved it as autoexec.cfg.txt Take a look at it and see what extension it has. Otherwise, you may have not put it in the right folder or used Word to edit it and Word puts in extra characters that make it too big. Use Notepad to edit or create anautoexec.cfg.
Couldn't load GFX.WAD: Quake is not installed properly. You need to reinstall it. It's that simple.
z_malloc: This is the QuakeWorld version of the Quake 2 error SZ_Getspace. Your aliases or configs are too big. Tone it down, break it up. Stop trying to stuff it all into one file.
couldn't exec autoexec.cfg: This message is generic. It gives this message in every case unless you actually have an autoexec.cfg. It's simply telling you it didn't find one.
A required .DLL file, GLIDE2X.DLL, was not found: The OpenGL32.dll file that is installed with the game is old. VERY old. Delete it from your Quake folder. It has no bearing on running Glide, the game does not run in Glide. Just delete the file and start again. The game will default to your Windows\System folder and find the driver for your video card there.
server uses protocol X "X" being any number such as 45 or 48: That is the numbering system identifying the point releases. For example 45 is point release 1.17 and 48 is point release 1.27. At this time, not all servers are running the same version. You will need to make a choice which version you want. They are not compatible.
version 4, expected 3: This means your point release installation was not completed properly. Somehow was interrupted. Reinstall your point release.