heh... make sure you have half life folders. to do this u have to first launch half life and let every thing update and load to the main screen.
then install 1.2 full client install or 1.2 lite install.
then install 1.2.1 beta patch and point it to the C:\Program Files\Steam\SteamApps\your email\half-life.
if done correctly it will go then look like this :
C:\Program Files\Steam\SteamApps\your email\half-life\esf
if for some reason its having trouble seeing the 1.2 then you have to go to start menu, control panel, add and remove programs and delete 1.2 and your 1.2.1 patch. and reinstall or redl them. because it may be file corruption.
make sure after uninstalling that the esf folder is indeed gone. (if not delete it). reboot > install > play.
hope this helps ya