Exchange 2003 in a cros Forest

Hi,

we want to install two windows 2003 Forests (AD) each with their own Exchange 2003 server. There will be a two way trust between them. Is it possible for users of forest A to browse the global addressbook and share their calendar with users of forest B?
Have you heard about a tool to make this happen? Is there a way to do it with OWA or over IIS? The Exchange Repl-tool is replicating the public folders between the two Forests but I couldn’t find a solution for the calendar and global addressbook.
Thank you for your help
kay