I ran into a great post on Ajaxian the other day, and came across a javascript Date library. The only thing was, this wasn't your regular run of the mill, calendar pop up, lots of scripting library. This was a ninja library. I library that picks up your form dates, breaks them and half, chops up the pieces and eats them for lunch. The demo is extremely awesome. Here's a quote from the site itself:

"Datejs is an open-source JavaScript Date Library.

Comprehensive, yet simple, stealthy and fast. Datejs has passed all trials and is ready to strike. Datejs doesn’t just parse strings, it slices them cleanly in two."

Pretty similar to my own description I know. See the Ajaxian article for a brief summary, then check out the site. I guarantee you won't be disappointed!