go in your main UT2003 folder, get in /system/ and open the UT2003.ini file. now get to this part:
Code:
...
[Engine.Engine]
RenderDevice=D3DDrv.D3DRenderDevice
;RenderDevice=D3D9Drv.D3D9RenderDevice
;RenderDevice=Engine.NullRenderDevice
;RenderDevice=OpenGLDrv.OpenGLRenderDevice
;RenderDevice=PixoDrv.PixoRenderDevice
AudioDevice=ALAudio.ALAudioSubsystem
NetworkDevice=IpDrv.TcpNetDriver
DemoRecordingDevice=Engine.DemoRecDrive
...
-put a ; in front of RenderDevice=D3DDrv.D3DRenderDevice
-remove the one in front of ;RenderDevice=OpenGLDrv.OpenGLRenderDevice
-save and run UT.
some of those options might not be there (like the PixoRenderDevice) because I use UT2004 but UT2003 is similar. If you can't find the OpenGL line... then UT2003 didn't support it ( but I doubt).