Okay, thanks to Phil’s feedback I have rooted out a couple of major problems when running on PHP4 and when you’re running the WordPress server on Windows. The fixes were just a few single line code changes here and there, so nothing too much to worry about, though I would recommend you upgrade from 1.3 since it will keep you up-to-date.
I can’t promise that I have fixed everything with the new parser in every possible configuration, but the plugin will now run much better in configurations running on PHP4 and Windows.
BTW: If you are still running PHP4, you really should consider moving to PHP5 as soon as possible, since WordPress is going to be dropping support for PHP4 altogether next year (about time, really!). I believe the majority of web hosts now provide a very quick and easy way to upgrade your server to PHP5, and it should only take a couple of minutes to do.