Restrict Input Start and End Dates to One Quarter

Hi all,

I have the following code:

sDate = Application.InputBox("Please enter the start date for " & _
"the date range of the data that you want to copy (d/m/yy).")
nDate = Application.InputBox("Please enter the end date for " & _
"the date range of the data that you want to copy (d/m/yy).")

How do I restrict the input sDate and nDate to the beginning and end of Q1, Q2, Q3 or Q4?

Thanks,
Gos-C