Looking for a cleaner solution to applying user policies, based on OS.

I have user groups that may be running either XP and Win7.
At the moment I specify a filter for the OS in each individual policy. Each policy is in a policy group say 'Admin Win7 policy group' and applied to the group 'admins'. But so does 'Admin XP policy group'. This means the correct policy gets applied but in the agents "Show Properties/Policies" I get "Non-Effective" messages for policies that get trapped by the filter.

An enhancement request for an equivalent to the 'dynamic workstation group' - 'dynamic user group' perhaps?