I’ve answered a question on StackOverflow (actually on SuperUser) regarding Finder and Samba shares on Ubuntu Linux. It’s only Ubuntu which has this problem, Finder works perfect with Samba when that Samba is installed on Debian, CentOS, …
http://superuser.com/questions/283863/force-finder-to-log-in-as-guest-to-a-smb-share/300382#300382