[eluser]Myles Wakeham[/eluser]
Have you had a look at the source in date_helper.php to see what could be going on there? I believe there are differences in date handling with PHP depending on whether you are running on Windows or Linux, and a lot of it has to do with the date range that you are dealing with (ie. I believe under certain PHP versions, dates < 1970 on Windows are not supported?). Anyway the source code is right there. Add some statements in the helper to let you see what is going on, and it should tell you what the deal is.
I use it in my apps with XAMP on Windows and its working fine for me.
Myles