i dont know if you got this prob fixed but this might work...
first open two windows in c drive then type this in one of the address fields:
C:\WINDOWS\system32
then in the other one type this in the address field:
C:\Program Files\Steam\SteamApps\mgagcc@hotmail.com\half-life\gldrv
now, in system32 look for the file labeled "nvoglnt.dll", without the "
copy it
go to the Half-Life folder then paste it in the gldrv folder.
After that you will need to modify the file drvmap so make a copy first.
In the file, type:
Default Default
gldrv/nvoglnt.dll OpenGL Driver
making that the only thing in the file, doing this will allow you to use OpenGL, the thing about steam is, it defaults to 3dfx so you have to manually change it.
I hope that helps...