searching for the number of occurences of a string

[M.N.A.Smadi]

hi;
say i have a text file with a string ( say '(XYZ)') and I want to find 
the number of line where this string has occured. What is the best way 
to do that?

what about if that string was say a 0 with leading and trailing white 
spaces, would that be any different?

thanks
moe smadi