cropping a string

hi all I was wondering if anyone had found a solution to the problem of cropping a string to a certain length...however a certain length based upon the actual "size" of it. By this I don't mean after n characters, or even after m words (have a function for this already)... what I'm looking for is function that will take a string and crop it down to a length dependant upon its size, ie. it would treat a w different to a l (apologies to those reading this on a monospaced client). I'm guessing such a function would take type of font (say, serif ot times) and the desired length in "standard" characters and then compare the string, translating each character into a length comparative with the standard character. I appreciate tha because of the nature of the medium that it becomes difficult to control how things appear on browsers, and that it would be nigh on impossible to make an *exact* function, all I'm looking for is something rough and ready which is better then counting chars. TIA, Tom