Shai,
If you follow the directions to use the "curl" command, you don't actually need to register for the data. You would need to use some dates that are within the past couple of days since this is real-time data, to use this particular data type with this command. For other available data, take a look at this page:
http://www2.mmm.ucar.edu/wrf/users/download/free_data.html
There are several links available there that will ask you to register.