Ok since this seems to be a problem for some people, here is the (hopefully) idiot proof guide to installing Open GL.
The best thing to do to avoid errors is have a fresh, unaltered System folder. Either that or reinstall the game and back-up your Cache, Music, Maps, etc. Also, make sure your DirectX is fully updated:
http://msdn.microsoft.com/en-us/directx/aa937788.aspx
You will need to determine what patch version you currently are using (224, 225, 226, GOLD). As far as 224, 226 and GOLD are concerned, it is very simple.
First, find the patch you need here (225 users, wait up. DL the patch, but don't forget CookieMonster's tutorial towards the bottom. You should really read it first):
http://www.oldunreal.com/specialpatches.html
Should look like this, find the V0.2.exe's if possible.
Download and install the patch, run it, MAKE SURE it goes to the directory wherever you have Unreal installed. Some people have it installed in Program files, others in just their main drive. If you are insecure, copy the patch into the SYSTEM folder of your Unreal, then run it.
Let it run, it will install everything. Once finished you will notice your Unreal.exe (Launcher) will be green, also a "backup" folder will be created in the System folder, this is all the original .dll's and such in case of any error.
Fire up Unreal, you most likely will get a splash screen, select for OpenGL rendering:
Once in Unreal all your video settings will have changed. Hit Tab Type Preferences.
Make sure the following is correct:
Once verified true, change your resolution back to normal and adjust brightness. (NOTE: If you have unusually low light, you will need an OpenGL Tweaker like Rivatuner
http://www.guru3d.com/category/rivatuner/).
You now have openGL installed! Now I'm sure you will want to tweak it and understand how it works (hopefully)
Check out this:
http://www.oldunreal.com/patch/Oldunrea ... update.pdf
OK, for the 225 users, this is a little more technical as you have to make some manual modifications. They are NOT hard to do.
Here is CookieMonsters complete guide to getting it working:
http://www.densdomain.com/Uploads/Openg ... torial.pdf
For 227 users, 227 COMES with the OpenGL patch. You just need to select it from the list after applying the 227 patch:
Select the following Audio Device, unless you absolutely must have AL:
Run the game! Pretty simple huh?
For those of you who want to have the capability to run 225 and 227, read this:
http://www.oldunreal.com/wiki/index.php ... nd_227_.3F
Enjoy
EDIT:
OpenGL is naturally darker in appearance mainly due to the fact that it uses dynamic lighting much more efficiently, therefore making dark spots in some maps even darker.
For those of you who are having problems with brightness, make sure the following is correct and make adjustments as necessary
like to change settings in the .ini's themselves, so you will need to go to your system folder and click Unreal.ini [Important! Opens with notepad. If you get an Acess Denied error, right click it->Properties->Change->Notepad]).
Don't forget to save after making any modification in the Unreal.ini!