On my Win XP, with Symbol, the PSI character is 89.
This code will insert the value:
Code:
Sub LetterPSI()
ActiveCell.FormulaR1C1 = "Y"
ActiveCell.Font.Name = "Symbol"
End Sub
Put it in the Personal Macro Workbook. Save it.
Then right-click the toolbars and choose Customize. In the middle tab, on the left choose Macro, on the right, click on "Custom menu item" and hold down as you drag to a toolbar (when you see the dark vertical line, release the mouse).
Then right click it and choose "Assign macro" and select this one. Right-click again and change name to something like PSI. Click OK.