I dont personally give a damn if it's on LAN or not.
the best way to hack is to exploit the vulnerabilities.
Use Nmap as the port scanner, try discovering more ports, I wud suggest you to use the command line instead of Nmap GUI (Zenmap) .
and i m sure if the OS is xp ( sp1 or 2 ) , you can get a hell lot of exploits from the net ( www.milw0rm.com
Discover the other softwares installed, check if their exploits are out. try exploiting IE6 , IE7
and no wonder u can get the shell out of it .
Try not physically accessing the target pc ( if u r concerned about knowledge)
though these are the script kiddies' methods obviously as u use exploits created by other hackers but that is it, u can't help it unless you start coding yourself.
For more on netbios (139) and microsoft-ds (445)
see this video on youtube , it might help