Directory services in a mixed environment (OSX, Windows, Linux)

Can anybody shed some light on a good practice of how to tie together machines with three different operating systems? ?If it were a completely windows environment, Active Directory would be a no?brainer. ?But we all have mixed?environments: accounting has to be on windows, POST has to be on OSX and CG could be linux or windows.

Some people I have talked to, suggested running a Windows Domain, and joining all other OS's to active directory. ?Others have suggested an openLDAP solution. ?I don't think open direcotyr is a viable

Suggestions, best practices, or guides would be very helpful.

thanks,