Just to explain one point above....
using \\ip.ip.ip.ip is a UNC share, you are telling Windows to open that device using SMB/CIFS and scan it for public drive shares. This will not connect with a web site which is a totally different protocol and port (HTTP:80 instead of CIFS/SMB:445)
Depending on the version of Windows, IE and the settings you have enabled, it may "guess" that it is really a web site, but it is not normal to do so - you have explicitly told it to open a drive share, you may even get an Explorer window with the public/user_1/user_2 shares if you put the right password in!
If you had dropped the \\ it would probably have found it. But to be certain, and not rely on Windows "guessing" things, put the whole path in "
http://ip.ip.ip.ip" note they are forward slashes, very different, and you are explicitly defining the protocol to use and therefore the default port.
Authentication for the web site is not based on SMB, Lanman or NTLM, it is straightforward HTTP forms authentication.