When managing application access in Mac OS X Server version 10.5, the settings under the Applications tab only apply to Mac OS X 10.5 Leopard or later-based clients. The settings under the Legacy tab only apply to Mac OS X 10.4 or earlier-based clients.
It's possible to manage both the settings under the Applications and Legacy tabs in Workgroup Manager for the same record. Doing this will allow Leopard clients to use the newer application access controls (under the Applications tab), while also allowing 10.4 or earlier clients to use the previous application access controls (under the Legacy tab).