Well this would work but be careful as this method is NOT exact.

i.e. It will look for 2403 so values like 2405, 2406 etc would not be found and it would say so, but if you did not code otherwise and it only had 240 that would be found and valid as well.

 Code:
Break On
If InStr(ReadValue('HKLM\HARDWARE\DESCRIPTION\System\CentralProcessor\0','~MHz'),'2403')
  'Value found' ?
Else
  'Value not found' ?
EndIf