first off, i HOPE u installed ESF over an existing half life installation. [yes it is possible to install it over something else, i did it over a retail counter-strike install, and it worked, not reccomended] you will find a file which should be located in ur esf directory, mine is here: C:\SIERRA\Half-Life\esf\
the file name is config.cfg. open it up, if windows asks u what u want to view the file with or what u want to use to open the file use notepad. at the very bottom [if its not anywhere in the config file already] type cl_fxquality 0 [mine is at 3, just bcuz i rule =D] and make sure its on its own line, not after another variable. then close it and save it. try that. i hope this helps.
*edit* disabled smilies so my directory location wouldnt hav a stupid face in it