I had the same issue. I wanted to use a checkbox and not option button
because option button control ever option button on the sheet. This is how I
was able to use checkboxes and have it when box A is check, box B become
unchecked.

Using a Forms Checkbox

Link your two checkboxes to their respective cells.
Checkbox A with A1
Checkbox B with B1

Then on Checkbox A us this code:

Option Explicit
Sub Checkbox_A()
Dim myCBX As CheckBox
Set myCBX = ActiveSheet.CheckBoxes(Application.Caller)

If myCBX.Value = xlOn Then
myCBX.TopLeftCell.Offset(0, 1).Value = False
End If

End Sub


Then on Checkbox B us this code:

Option Explicit
Sub Checkbox_B()
Dim myCBX As CheckBox
Set myCBX = ActiveSheet.CheckBoxes(Application.Caller)

If myCBX.Value = xlOn Then
myCBX.TopLeftCell.Offset(0, -1).Value = False
End If

End Sub


This will do the trick. I was tired of everyone telling me to use option
button so I did it myself.

p.s. - to not see the "TRUE/FALSE" under the checkboxed, just change the
color of the text to match the background

~Ryan
--
Silverbird Designs @ www.silverbirddesigns.com

Fighting Texas Aggie Class of 2009