In Windows, is active directory required for using "Domain" instead of "workgroup"? Do I need to register a domain with a DNS provider like godaddy?

What I really want to do is set up my home LAN so that everyone connecting to the main router (which is everyone, which is about 30 people) can see each other.

I've tried having everyone use the same work group name, still hit or miss. I tried setting the domain name and host name on the router itself, still nothing. I've tried joining the domain name I set instead of work group, and I get an AD error.

But ideally, everyone who is connected to the main router should simply just see each other and any shared folders.

I've had this problem when I was not the network admin on other large LANs, and I've never been able to figure out why sometimes people disappear or never see each other.

I'd really prefer using the native sharing functionality in the OS to setting up an internal FTP or Samba server, etc.

Any sure-fire ways to fix this? (maybe an open source clone of AD?)

Thanks!