Are you using Static or Dynamic IP Addresses that is one question you need to ask. If you are using DHCP on your network you will have to setup Solaris to request an IP. If they assigned you a static then you will have to add an entry to /etc/hosts, /etc/hostname.xxx, /etc/defaultrouter, /etc/resolv.conf, and change a setting in /etc/nsswitch.conf. You will also have to check if your site uses a proxy server for web access.
As someone previously stated you cannot join a Windows Domain without third party software. Samba is a free alternative that should probably suit your needs if all you want is to access shares, however, if you want to perform user authentication to a PDC then you might need to setup Kerberos or something to communicate with AD.