[Samba] Newbie group mapping question

[Ninti Systems]

I'm wondering if, in a context where samba 3.0.4 is PDC for an NT domain
with XP clients, it is necessary or at least normal practice to map
most/all NT groups (eg Domain Admins, Domain Users) to unix groups?

Also, I notice when I do 'net groupmap list' that there are not only
Domain Admins, Domain Users and Domain Guests, but also plain Admins,
Users and Guests. What is the significance of these two sets of groups
(the Domain groups and the 'plain' groups), should I map to one or the
other or both?

Sorry, my knowledge of Windows is even less than my knowledge of Samba
at this point in time.

Thanks
Mick