The correct thing to type in the C shell (csh or tcsh) is
set path = ( $path /new/usr/local )
If you don't put the parenthses in place, you will destroy your path and be unable to execute anything, as you have discovered. You must not have read Q43 in the FAQ list carefully enough.

You need to log back out and log back in now, to reset your path to whatever the system has for your default. You can then enhance that path with the extra things you need for AFNI. When you have that working properly, you can then add the appropriate command to your .cshrc file. If you don't know how to setup your .cshrc file, I suggest that you find someone at your site who knows about Unix/Linux and get her/him to enlighten/educate you.

bob cox