I wrote following code:

Private Sub Worksheet_Change(ByVal Target As Range)

If Target.Column = 2 And Target.Value = 100 Then
Cells(Target.Row, 3).Value = Date & " - " & Time
Target.Value = Target.Value / 100
Target.Style = "Percent"
End If

End Sub

The idea of this is when i enter value 100 in column B, then timestamp is
inserted in column C.
I know this code sux - last 2 rows of this code were written cuz i didn't
know how to triger this macro by entering value - 100%.
I want to know:

1) how do i triger a macro when value 100% is entered? I mean 100 is entered
in cell which is formated as % ?
2) how do i format my timestamp so it enters date & time and then i can add
rest of the formating through cell formating ? For example when i enter date
and time by pressing ctrl + ; then space and then ctrl + shift + ; i get
"date time" and after this i can format this datetime as i want. But after i
get the same through macro excel does not respond to formating.
3) i want to add last modified timestamp in column 5 which would trigger
each time value is entered/changed in column 2 how do i do this ?