Tenebrae is not quake1 anymore, it uses more advanced graphics algorithms so it
requires a much faster system to run.
These are the bare minimum reqs to run Tenebrae:

PIII 600
64 Mb RAM (More if you want to use some mods.)
Geforce1
Quake1 data (registered or shareware)
Water vissed maps

Recommended is a faster processor and a geforce4 / radeon 8500 class 3d card.
Tenebrae_Readme.txt contains full list of supported video cards.

WWW:	http://tenebrae.sourceforge.net/