You could try adding this to your .vimrc:
autocmd BufNewFile *.c 0r!new_c_file
and adding this file (named new_c_file in my example) somewhere in your PATH:
echo -n "/*
* Hello, I'm a new C file
* Begin date: "
echo " */"
This only inserts the text when you're editing a *new* (previously nonexistant) file ending in .c
The manual suggests putting autocmd! before the autocmd line in your .vimrc, as there are apparently circumstances where the .vimrc could be sourced twice. autocmd! drops all previously set autocmds so you don't set one up twice.