In Windows XP the memory offset assigned is virtual memory, it is relatively only to the application that is currently running. There are ways in windows of sharing memory, one sech way this can be done is through a DLL file which delcares shared memory segments.
Also, if you have permissions to access the memory block of another application I believe there is another way of doing it, but i could not tell you how that is done offhand. Checkout
http://www.thecodeproject.com, they probably have a tutorial on there for doing it.
Good luck.