I have a pc running windows 2000. The PC is in a workgroup, not a domain. It operates some medical equipment so I cannot change the way users login without major manufacturer license key problems.
I have samba installed and I can see the linux box from W2K box and the shared folder. I can even read. But I cannot write. The folder on the linux box is chmod 777.

My smb.conf has writable=yes, public=yes, and security=share

Are you trying to write to existing files on the public share? If so, make sure the permissions on the individual files are also 777. Executing chmod 777 on the directory will not change the permissions on the individual files in the directory unless you use the recursive switch, which I believe is either -r or -R.

Can you create files on the share but then not write to them? That would mean that new files being created are not world writeable. In that case, there are some options for the smb.conf file that could correct that.
You might be able to use "force group" to make everyone that connects default to whatever group you choose. I'm not sure it that will work with share security.
There are also some mask options that will set the permissions on any new files or directories you create. I don't have a Samba server in front of me but I beleive it's something like dmask or directory mask. If you look at the man page or help files on smb.conf, you should see the options I'm referring to.

If it's none of the above, what error messages are you getting?