To compile pnet.c under Linux (9.04 Ubuntu) in Matlab 2009b you must make sure the comments // are changed into /* ... */
// Comment Line
/* Comment Line */
it only gives me a warning
Warning: You are using gcc version "4.3.3-5ubuntu4)". The earliest gcc version supported
with mex is "4.1". The latest version tested for use with mex is "4.2".
To download a different version of gcc, visit http://gcc.gnu.org