Forecasting student participation

I have data for workshops conducted by my department where students show up and meet with peer advisors.

The data I have is from 1996 to 2005, with specific date, day of the workshop and the number of participants who showed up.

I want to forecast the future student participation for the month of august 2007? For understanding this concept (as it is new to me) I have shortlisted the total number of participants for only the month of august for each year from 1999 to 2005.

How do i go about acheving this forecast?

thanks in advance

excel file is attached

thanks ray for the reply,

is this correct?

=FORECAST(x,known_y's,known_x's)

where

known_y's = years

known_x's = totals

what do i enter for x ?