to play on battle.net use the Star-key.exe
program to obtain a valid CD-Key when installing 
starcraft...  If 2 persons with the same CD-Key
are on battle.net at the same time, only the
first person logged on will get to play.  This is
the case unless you register with the company with your
name & stuff online (not required), then battle.net will
look for your registered name...