http://blogs.technet.com/asksbs/archive/2008/07/05/troubleshooting-high-memory-usage-by-a-msde-instance.aspx
I asked around and in general the rule of thumb most use is as follows:
http://msmvps.com/blogs/bradley/archive/2007/12/25/adjusting-sql-embedded-instances.aspx
MSFW 128WSUS 256 (per Dr. J's blog)SBSMonitoring 70SharePoint (I didn't tweak this)If CRM is on the box, then limit SharePoint to 384
Read the complete post at http://msmvps.com/blogs/bradley/archive/2008/07/06/throttling-those-instances.aspx