Many customers have been asking for the support of SQL 2008 R2 and Operations Manager 2007 R2.
Today we relased a KB on how to do a clean install or an upgrade to SQL 2008R2 while running Operations Manager 2007 R2.
KB Link is : - http://support.microsoft.com/kb/2425714
Be advised the KB ONLY covers Operations Manager 2007 R2 and NOT SP1 installations.
For the Audit Collection System (ACS) it's not supported to do an upgrade, only a new clean install is supported.
More info can be found at the Operations Manager Team Blog: http://blogs.technet.com/b/momteam/archive/2010/09/28/om2007r2-support-for-sql-2008-r2.aspx