Thanks for the input Ed. I am definitely more inclined to push for some new hardware after what you and Vassie have written. I hope to be in contact with MS sometime this week and will post what I find out.
It is interesting that something which at first glance seems relatively simple turns into such a large undertaking. It seems to me that this is not a unique situation. Companies get bought, sold and merged routinely. How do these businesses merge their network infrastructure - or do they? I don't have a great deal network expertise, but would it be smarter to make our domain a "sub-domain" of the larger forest than to make our domain disappear and become an independent OU within this larger forest?
Here's a little more background to the "big picture" and perhaps this will get a little more discussion going. And perhaps this will need to be placed into a different forum...but here goes...
This is a state governments project. Our state has a "centralized" IT department...sort of. We have a central IT office, but most individual agencies have their own IT department. The larger agencies have a larger and more developed IT department while smaller agencies may or may not have their own IT staff and are much more likely to depend on the central IT office. For better or worse there is some animosity between the IT departments as everyone has their opinion about the best way to do business and the best software to use. I'll stop with that so I don't end up writing a thesis about the pluses and minuses of centralized vs de-centralized IT departments. There is currently a state-wide project underway to centralize our email, calendaring and document storage systems utilizing MS Exchange and MOSS. The central office is promoting "single sign-on" to Exchange by bringing all user logins into their domain. This begged the questions, why not just setup a trust between our domains and will the users still be able to access servers in our domain? The answer were "we don't want the administrative overhead of maintaining multiple trusts" and "you can have a trust only temporarily while you bring all your servers into our domain." At this point this domain migration is "voluntary" if we (all agencies) do not comply we may be forced to comply.
So my question to anyone reading this is: If you were put in charge of merging multiple independent agencies, each with their own domains (Windows, Novell, ???, ...) into one centralized AD forest and allow for single sign-on to Exchange and MOSS what would be the best approach and have the least impact on 20,000+ employees, thousands (maybe tens of thousands) of diverse web, mainframe, client server and stand alone systems, thousands of servers, multiple SANS and mainframes, tens of thousands of PCs and mobile devices, etc, etc...?