First thing i suggest you do i make the form invisible during run time. you can eaily do this by chagining the visible property to false.
once this is done make a button on a separate tab which has the following code
Dim strInput As String, StrMsg As String
StrMsg = "Please Enter Password"
strInput = InputBox(Prompt:=StrMsg, TITLE:="User Validation", xpos:=2000, ypos:=2000)
If strInput = "stuff" Then 'strInput being textbox
tab.visible = true
End If
this will promp the user for the password "stuff in this case, but change it to whatever you want. if the password is valid the tab will become visible. If the password is invalid, then nothing will happen