Desktop Sharing by XP PRO

I have XP pro loaded and a Cable connection as from ISP at my Office. Now I have Dialup at my HOME also with XP pro loaded.

The question is if its LAN or Cable network in between two PC I can share my desktop. But now I want to share my Office’s Desktop from my HOME by my XP Remote Desktop Connection. There will be NO IP for Dial UP and If I put my Office IP from my home in Remote Desktop Connection it will not work cz Office IP is not live IP. Its internal IP of my ISP.

So How can I share my Office desktop and Home desktop vis-e-ver ?

Thank you in advance for accepted or non accepted answers.