Golf version, with validation tests and example to confirm length.
 Code:
Function IsNum($_)

  $IsNum = IIF($_ = Val($_), 1, 0)
  Exit 0

EndFunction

'123 ' IsNum('123') ?
'abc ' IsNum('abc') ?
'a23 ' IsNum('a23') ?
'1a3 ' IsNum('1a3') ?
'12a ' IsNum('12a') ?
'a2a ' IsNum('a2a') ?


$Id = '13293'
If Len($Id) = 5 And IsNum($Id)
  '5 digits!'
Else
  'invalid ID!'
EndIf
Glenn
_________________________
Actually I am a Rocket Scientist! \:D