Hey folks,

Anyone know of a way to restrict data entry in a cell to one of onl
four total possibilities?  More specifically, is there a non-vb
solution to restricting users from inputting anything into a cell wit
the exception of:
x X o O

These are lower and upper case of both the letters X and O (not Zer
the Number).  The particular range (if it matters) that I need thi
restriction in place is D4:F6.  

If you'll notice, the range is a 3x3 square.  The charactors in tha
3x3 square have to be either an X or an O (case irrelevent).  Yup, yo
know what that means.  TicTacToe :)