short note: combo drive isn't a drive that can write dvds. a combo drive just READS dvds. what you are searching for is a superdrive. the one in the powermacs is a standard IDE superdrive from pioneer. so you can just buy that one and build it into your mac. or you buy an external firewire version, like the one from lacie (
www.lacie.com).
i assume you're pro, so you're using dvd studio pro? but if you are working with idvd, then you would have to download a patch to get idvd to work with your superdrive.
this applies to external superdrives, but i don't know if idvd also refuses to work with internal, but upgraded superdrives? i don't know, but that's no problem anyway, cause there's this patch.