>Does anyone have a simple function that returns the last date available in a given month?

I think it's been posted before, but you can try this:

dv = date value to try

dv = DATE()
?DAY(GOMONTH(dv-DAY(GOMONTH(dv,1))+1,1)-1)

Gives you 31 for date value of 7/5/2000.