I have a spreadsheet the has in cell G11 a specific month. In G10, I need
the date for the last day of the month. For example, if G11 shows
February,
I need G10 to show 2/28/09 or 2/29/08 depending on if it is a leap year.
I
would also like the year to be the current year.

Go to the first day of the following month and subtract one:

LastDayOfMonth = DateSerial(Year(G11), Month(G11) + 1, 1) - 1