I have read a lot, but still can't figure out the best way to do this:

I have 60 cells aligned horizontally: (Jan-05 to Dec-09)
Above the dates I have a project cash flow.

First I need to report the date at the first occurence of cash flow (a
negative number).

Secondly, I need to report the date at the last occurence of cash flow
(a positive number).

This is so I could set up for the XIRR function. The problem is that
the cash flow appears in various dates and durations based on the
project parameters, so I can't lock the XIRR calc to specific cells.

Any help or guidance is greatly appreciated!