WickedGL?
Ok so im assuming you have a Voodoo 1/2/3/5 card?
If you have a Geforce family download detonator driver 21.83 from
http://www.nvidia.com
For Voodoo family heres the fix...
before installing wickedgl, rename your MOHAA demo .exe file to quake3.exe
then install the wickedGL. When it asked (if it even asks) where is quake3 just point to the demo you just renamed. Wicked GL will install just fine. However, voodoo cards will still see the ingame menus all messed up but game play should be ok...
Rename you quake3.exe file back to the mohaa demo orginal name...
Enjoy