In November I wrote here about problems executing maintenance plans due to Integration Services edition compatibility issues. Last night we released cumulative update #3 for SQL Server 2008 RTM, and it contains a fix / design change for this problem. You can read about it and download the fix here :

Cumulative update package 3 for SQL Server 2008

http://support.microsoft.com/kb/960484

FIX: Error message when you run a maintenance plan in SQL Server 2008: "The SQL Server Execute Package Utility requires Integration Services to be installed"

http://support.microsoft.com/kb/961126/