The following seems to work.

I created the textbox using "Developer - Insert - Textbox"

I opened the revelent macro module by clicking on Design Mode then right clicking on the text box and selecting view code.
Paste the text below into that window.

Deselect Design mode.

ENJOY.



Public oldvalue As Double
Private Sub TextBox1_Change()
temp = TextBox1.Value
If Right(temp, 1) = "%" Then temp = Left(temp, Len(temp) - 1)
If Not IsNumeric(temp) Then temp = oldvalue
oldvalue = temp

TextBox1.Value = Format(oldvalue / 100, "0.00%")
End Sub