Instead of using "Syntax" menu you can also manually source in the syntax file. Edit the file with gvim and at : (colon) command give 'so' command. For example -
gvim foo.pc :so $VIM/syntax/esqlc.vim
Each syntax file supports one or more default file name extensions, for example, JavaScript syntax file supports the *.js extension. If you happen to use an extension that conflicts with another default syntax file (such as adding JavaScript to a *.html file) than you can source in the additional syntax file with the command :so $VIM/syntax/javascript.vim. To avoid all of this typing, you can create a soft link like -
ln -s $VIM/syntax/javascript.vim js gvim foo.html (... this file contains javascript functions and HTML) :so js