also Richards, IPDecimal() can return this information too.

Code:

Call 'g:\kix\udf\IPDecimal\IPDecimal.kix'

      ; Get primary NIC details
      $IP=EnumIPInfo(0,0)
      $Mask=EnumIPInfo(0,1)

      ; Calculate info
      $Network=IPDecimal($IP) & IPDecimal($Mask)

      ; Display it
      ? "This computer is on network: "+IPDecimal($Network)