Came across this very useful article and FAQs about SCCM in a multi-domain or multi-forest scenario. http://blogs.technet.com/b/configmgrteam/archive/2010/07/09/frequently-asked-questions-about-active-directory-domains-and-forests-with-configuration-manager
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Read the complete post at http://t3chn1ck.wordpress.com/2012/01/27/faqs-about-active-directory-domains-and-forests-with-sccm-2007/