Several Months ago we migrated from exchange 2003 to exchange 2007 everything went very well. Exchange 2007 is functioning well and the uninstall and removal of the 2003 server I thought went well. I ran the best practices analyzer and the admin group for the exchange 2003 server is still there. How can I remove this group from the organization? The old 2003 exchange server successfully uninstalled exchange no issue and was demoted from the domain.

I would leave it alone. Its only cosmetic. http://technet.microsoft.com/en-us/library/bb288905(EXCHG.80).aspx Microsoft strongly recommends against removing the original Administrative groups from an organization. If any of the original Exchange 2003 or Exchange 2000 administrative groups have been removed, verify that mail continues to flow and does not build up in the System Attendant mailboxes on Exchange 2007 servers. Also, verify that public folder Free/Busy information is updated successfully for Outlook 2003 and earlier clients. If mail builds up in the System Attendant mailboxes, or if Free/Busy information is not updated successfully, the LegacyExchangeDN attribute of the affected user(s) may point to a deleted Administrative group. In this situation, you must change the LegacyExchangeDN attribute for the affected users.

I will take your advice and leave it alone. It certainly isnt hurting anything the enviroment is running very well. queues are clear and free busy anad all works well.