When we program using dates and times here in the office, we almost never deal in date strings except for output purposes. Internally, everything is done using "seconds since the epoch"-type timestamps (the value returned by time() is an example) and then common modules are used to convert from these timestamps into strings. Even if you can't install these modules (which, really, you should at least convince your boss to install either Time::ParseDate or Date::Manip), you can do most of the work yourself using localtime(). The only place that becomes hairy is when you're dealing with daylight savings time.

Seriously consider ditching the whole 30Nov00 way of passing dates around in your script query string and replace it with the timestamp for that date. For one, '00' isn't Y2K compliant, and two, you'll have a common format you can use for addition, comparison, and conversion.