Apple have confirmed that the latest Mac OS X Leopard release, 10.5.3, fixes the GPS-CS1 support issue. If you raised a bug with Apple reporting this issue, you should have an official response.
Readers of this site have also confirmed that both Intel and PPC versions of 10.5.3 now support the Sony GPS-CS1.
So... if you are a PPC user, upgrade to 10.5.3. If you have an Intel Mac, Leopard owners should upgrade to 10.5.3. Tiger owners may wish to try the previously reported workaround.