I had an interesting post @ forums.iis.net about adding the IIS_IUSRS group (replacement for IIS_WPG)  to a SQL Server 2005 local server.  If you try to add the group using MachineNameIIS_IUSRS it errors.  If you put BUILTINIIS_IUSRS.   That works.  Here is the post.  http://forums.iis.net/p/1148362/1865423.aspx#1865423

Cheers,

Steve Schofield
Microsoft MVP – IIS