You can't "map a network drive" in Mac OS X because you're not using Windows anymore. "Mapping a network drive" is something that happens only in the Windows operating system. If you want to map a network drive, you will need to use Boot Camp to boot your Macintosh into the Windows environment, if you have one installed.
Under Mac OS X, you can connect to a network share by visiting the "Go" menu in the Finder's menubar and either selecting "Network" or "Connect to Server..."
If you select the former, you will be presented with a Finder window displaying all computers within the configured network. If you select the latter, you can type in a connection string such as "smb://servername/sharename" where "servername" and "sharename" are the server's name and the share you wish to connect to.
