I just bought this wonderful game, but unless I'm missing something there doesn't seem to be any kind of modern-day resolution option anywhere? Just like the non-GoG version, the weird tiny res used by Outcast messes up on today's monitors. On top of that, the basic Windows 7 Aero theme also doesn't seem to like it.
Am I overlooking an extra settings or patch executable somewhere?

I have heard of a 640x480 patch, but have no personal experience with it.
Keep in mind that this is a completely software rendered game. At its highest resolution (512*384) it brought machines of its day to their knees. If you were to raise that to 1024x768 -- twice as large each way, four times as many pixels -- you would need four times as much processing power.
Of course, we've GOT four times as much processing power now, so it would really be nice to see it in high res glory...
EDIT:
Trying to locate said patch, I ran across this:
http://and.intercon.ru/index.php?id=releases (search page for Outcast Lives Forever)
It's just a map viewer, not a game, but should be pretty (I'm on my netbook and haven't tried it yet, so I can't make any recommendations or warnings or any other kind of statement)
OK, finally tracked this down:
<quote source=http://www.rage3d.com/board/archive/index.php?t-33865846.html&gt;
The only way to get the patch that increases resolution working is running the game in Win98, since the resolution patch doesn't work in 2K/XP.
This resolution patch can play in WinXP normally. (may be with compatility mode or something i can't clearly remember) + Update Patch
http://outcastii.free.fr/FTP/loaderp_eng.zip
Outcast loader + (159 KB) - Now you can play to Outcast in 640x480. VB6 runtime is needed : vbrun60.exe. << DEAD LInk for VB6
http://www.outcastii.net/
Great Fansite.
</quote>
AAAND one last link to a forum that has various links:
http://www.openoutcast.org/board/viewtopic.php?f=16&amp;t=756&amp;p=6431&amp;sid=445108be321401e5438b94676d2c967e
And at least one place to get the 640x480 patch, which unfortunately won't work in 2000/XP/Vista/7 :(
http://www.simeon-carstens.com/ (you may need to translate it from German)
(Actually, it apparently works even on Win7 64bit (for some people) if you set all the EXEs to Win98 compatibility mode and then use the normal launcher -- but it also apparently crashes a lot)
OK, wore myself out there. Will post later if I actually get anything working at higher res :)

A minimum of 640x480 would be already be a godsend, because in full screen I get a small gaming window at the left side of my screen with rest of the screen completely black, and my Windows 7 aero theme temporarily corrupts. It's playable, but only just.
In windowed mode I get a teeny tiny gaming window at the center of my screen which renders the game totally unplayable - it's simply too small to make anything out!
Any way to get around this? One would assume that if there was a 640x480 patch that GoG would have included it in this release to make the game playable on current systems...

I think that the main problem with the 640x480 patch is that it caused some instability. Haven't tried it myself though.

The 640x480 patch is available from the site of the author:
http://simeon-carstens.com/privat/outcast/patch.exe
(readme inside the self-extracting archive)
I will try it myself soon and post my experiences.
EDIT1: When running in WinXP with Win98 compatibility mode this patch works fine. 640x480 fullscreen. I also had sound issues which could be fixed by turning the sound acceleration to minimal (via dxdiag).
EDIT2: I found some tweaked config files which again improved the picture quality. It is mainly about the the LOD, bumpmapping, AA and viewrange settings.
Originally done by someone called "Crazy_Bon" in the 3dcenter.org forums. Simply rename the the file to a rar one and replace the inis in your Outcast folder (make a backup first!).

I remember from my experiments with trying to replay the cd version of the game a few years ago that it was possible to edit certain files in the installation directory and set a higher res. Although at the time it was unplayable on my system so i never got much use out of it.

I cant remember the name of the files exactly, but if you try opening a few in notepad it was pretty obvious if i recall.

Well, I had a look around and I found screen settings in the file called OUTCAST.ini in the installation folder. I changed screed_width to 640 and screen_height to 480 and at least the game window is now in the center of my screen when I run the game. Still big fat black borders all around of course, but it's better than nothing :)

Is the game window really small?

ok. cheers for the reply.

Unfortunately with Appeal being dead since 2001, I doubt anyone on this planet has functional source code of this game. I bet it is technically impossible for gog to introduce higher resolutions etc.

Might be a stupid question, but have you tried to reduce your desktop resolution to something lower than 1440x900 and closer to 512*384ish before launching the game ?
That would at least reduce the size of the black borders and augment the physical size - on your monitor - of the game "window" / visible area ...

Works fine here on Windows 7 Ultimate 64 bit. I am now playing Outcast in 640x480 resolution. I had to turn on Windows 98/ME compatibility for all three Outcast executables (oc1|2|3.exe), and checking the "run as administrator" tag. I have only tested for a few minutes though, so I don't know if it remains stable, but it has worked well so far.
Thanks for the links!
One more thing: no one has asked about it yet, but in case anyone is trying to run the game on a machine with more than one ATI Radeon graphics core (such as Crossfire or a two-core card), you will want to turn off the Catalyst AI first in the graphics card control centre, otherwise you may experience flickering in the image. The same goes for a lot of games from this era, so if you ever experience screen flickering on a Radeon card, kill the Catalyst AI.
Edit:
Also turning on Cinemascope mode in the Outcast loader removes the black edges and makes the game fill my 24" widescreen monitor, except for the lower portion of the screen. Looks great!

It works for me too, the hud is a little messed up but it's playable, good news as a lot of LCD monitors need at least 640*480 to show fullscreen (well at least it's the case of my 22").
Let's hope it will remain stable.

Yep this worked great for me, its now loading full screen and running smooth as butter. Thank you!
Btw im on XP if that makes any difference, i did just as you said and tagged all the exe's as win98 compatible, piece of cake!