WSS/MOSS RTM & SP1 is not supported on WS2008 R2. It is supported with SP2 though. More information can be found at

http://blogs.msdn.com/opal/archive/2009/05/08/install-moss-2007-wss-3-0-on-windows-server-2008-r2-you-will-need-sp2-slipstream.aspx