Depends on what version of Ubuntu you need to use.
The Samba version is what really matters.
To become a member of Active Directory, you would join the server as described in the documentation for Samba. Then Google how to either become a member server, or clone its data from the ADS, and then reconfigure the smb.conf to be standalone.
To do it without Windows Active Directory (or just domains for NT4 servers)
create the server with a wizard if your not sure, or edit a sample smb.conf in the help/documentation to your requirements (also known as standalone server mode).
It uses LDAP or NIS for its services. (depending which way you choose to setup)
Zentyal has server software (and was based on Ubuntu, previously known as EBOX)
could be worth looking into.
Maybe if you are stuck for which way, always consult Google first, then the Ubuntu community. This way I can assure you you would save yourself some time, plus you are more likely to be helped more quickly if you did some research first.
Anyway for client computers and servers (depending on what OSs you're planning to use, here's a list "based on my personal experience only"). It comes with no warranty, guarantees, it could be fit for reference of my experience, but not for purpose as things change fast in Linux/Ubuntu/Samba.
With that said, here is that list I mentioned.
NT based Windows versions
• Windows XP Professional / Media Center editions
⠀• (works both ways for joining networks, home editions doesn't do server connectivity)
• Windows 7/Vista
⠀• (could work both ways, but needs registry changes to use the standalone properly, but can make the OS slightly less secure.)
• Windows Server 2008 & 2008 R2
⠀• (join its domain, clone the ADS @where possible@ and then unjoin by reconfiguring it to be standalone, using smb.conf @cannot be used as bdc to samba@
(well, unless there's been changes since I last checked, but to my knowledge,then no, it cannot.)
• Windows Server 2003
⠀• (can do same as Windows Server 2008, but has the ability to join either methods, as it's from same code base as XP)
• Windows 2000 Servers
⠀• (the standalone is almost the equivalent of a 2000 Active Directory)
• Windows 2000 Pro
⠀• (can join both but I think it would need for newer ADS versions to be in compatible mode @sometimes explained as not secure@ )
• Windows NT 4.5 Back Office (the upgrade discs, technically not an outright standalone OS)
⠀• (it doesn't have active directory, but used a service before ADS was born called "Back Office", use this reference as the same as NT 4 server)
• Windows NT 4
⠀• (standalone method only, nt4 doesn't have ADS as far as i know)
• Windows nt 4 Server
⠀• (same as above, but u can join the Ubuntu to a nt4 domain, and set Ubuntu to be the PDC, and the NT4 as BDC if you wanted)
• Windows NT 3.x (server)
⠀• (standalone only, I don't know if it can be the PDC to Ubuntu, I think it's BDC to Ubuntu only due to its age)
• previous versions of Windows NT
⠀• (I doubt you use them, and would think it's irrelevant)
Non-NT based Windows versions
• Windows Milennium Edition
⠀• (no direct domain connections, but can use logons for profiles and remote shares, but is unsecured as the logons are in the registry as plain text, as far as I know.
• Windows 98 & 98 SE
⠀• (same as Milennium Edition)
• Windows 95
⠀• (same as Milennium Edition)
• Windows 3.1.1 for Workgroups
⠀• (technically not an OS, but can link for shares only, if used with network adaptor add-ons such as Novell Netware, which would require software equivalents for Ubuntu, or Suse software)
• Windows 3.1
⠀• (same as Windows 3.1.1)
Previous non-NT-based OSs than 3.1 - (highly irrelevant to you I would assume)