[OT] External IP Address?

[Martin Gallo]

I have a probably straightforward problem that I am not sure how to  
resolve. I maintain a small network of computers at my fiancee's  
office. She is able to access her practice management software from  
home just by entering the IP address provided by the ISP. For reasons  
not at all clear to me, the ISP is unwilling/unable to provide a  
static IP and so for the last two years I have been running IP  
Observer on the server - IP Observer checks the external IP address  
at routine intervals and emails a new address if it changes. IP  
Observer stopped working last week and I cannot get it to work any  
more, when it checks, it cannot find an IP address.

So, what I think I need to do is either find new software that works  
or figure out from code how to determine the external IP address and  
email it to my fiancee.

Can anybody provide a (Macintosh) software recommendation?

Failing that, how do I get the external IP address? I can se two  
different paths for this - either someone sends an email to a  
specific address that triggers an IP check/response cycle (using an  
automatic Apple Mail action) or the solution routinely checks for a  
change and emails it.

Help and sorry for the intrusion.

Marty