Excel 2010 'calculating 4 processors'

I am experiencing a slow down in Excel on a brand new machine with four processors, when I attempt to drag a slightly complicated formula down roughly 500,000 rows. The formula populates data in the first few rows then Excel crashes.
Has anyone else noticed this? A google search states it has something to do with the threading? Is this configurable in excel? Shoud I change the setting to use only one processor? Ideas? Suggestions?
Thanks,
GG