Windows Homegroup

Can I create or join a Windows HomeGroup? In Windows help it says
Computers must be running Windows 7 to participate in a homegroup

I know that FreeNAS has an option to be a Domain Controller, so maybe I should be looking at getting that setup.
Domain controllers are for, err, creating domains. Homegroups are something else, it's basically an extension to the traditional workgroups. And as far as I know Samba doesn't support it.
Actually, I was an administrator on a domain running IBM LAN Server supporting over 2000 users some time ago. I have little idea about what a Homegroup is, I just thought it was something like a baby domain. I just had another look at FreeNAS providing a Domain Controller service and there is something about Realms... Can't say I've heard of them previously.
Realms are typically for Kerberos. Active Directory is basically a mix of DNS, LDAP and Kerberos.