Public IP address

Hi,
Sometimes I?m away from the office and need to access the local (internal) FTP server. As the IP address is dynamically assigned by the ADSL provider, I always have to check for it b4 going out or phone the office and ask someone to check it for me. Sometimes I need it when nobody is at the office. We run the LAN (and the FTP server) behind a NAT/FireWall. I?d like to know if someone has any idea on how to write a program (maybe a script) that periodically gets the public address and publish it (sends a msg to a special email account) so that only authorized people can have access to it. The manual process I use is connecting to www.abusar.org. When the page shows, I get the public address at the top of the page.
Thanks!