Here's another question we get a lot so I thought I'd send out the scenario in case some of you had this question as well.
Hey J.C., I'm an SMS administrator at a rapidly growing widget manufacturer and for the last few years we've been buying out some of our competitors in other countries. When we acquire new companies we keep their existing forests instead of joining them to our network as a new domain. We do this for a variety of reasons, including the considerable amount of labor involved as well as the difficulty of physically managing those remote computers.
To the best of our knowledge, SMS creates sites within forest boundaries and it’s not possible to join more than one forest in one SMS site. Because of this we create our software packages several times for each forest or site but we really don't like spending our time doing the same job over and over again. Is it possible to create a package for multiple forests or are we stuck doing it the way we are now?
There may be a better way to integrate SMS into the new companies you acquire. A single SMS site can span multiple forests as long as all the SMS site systems are in the same forest and it is just clients that are in the remote forest. In this scenario, you need WINS to find the MP for the assigned site, and you need the Advanced Client Network Access Account defined for the remote forest clients to access the MP.
If the remote forests have SMS sites already in place, then they can be joined in a single hierarchy, as primary sites can be in a different forest in a hierarchy. Note that this does not apply to secondary sites as they must be in the same forest as the parent primary site.
For more information check out http://technet.microsoft.com/en-us/library/bb694003.aspx.
Hope this helps!