Here is an excerpt out of the script that I use. It is a quick and dirty way of dicerning where they are calling from. I actually use variations of this for both VPN and dialup uses:

$ip0=@ipaddress0
$ip1=@ipaddress1
$ip2=@ipaddress2
$ip3=@ipaddress3

IF ((SUBSTR($ip0,1,12)="xxx.xxx.xxx.") OR (SUBSTR($ip1,1,12)="xxx.xxx.xxx.") OR (SUBSTR($ip2,1,12)="xxx.xxx.xxx.") OR (SUBSTR($ip3,1,12)="xxx.xxx.xxx."))

(action to be performed)

ENDIF

Make sure that the ip entries that are made above use full three (3) digits for the octets. If the is only a single digit for the octet, preceed it with blanks -- otherwise it will not work.

Let me know how it works.