internet lookup

Is there an internet look-up function and if so how does it work. I need a function that will look up information from a website and then enter that numerical information into a cell of the spreadsheet. Specifically i want the function to look at online stock prices and then make computations using those prices. The program would ideally be able to do this with the user simply inputting the name of the subject company and the dates of the stocks. I would greatly appreciate advice from anyone on how to use such a function.

thanks a lot...
tom behrman