To make it more clear:

To my understandig with Schedule:At I can only run some system commands at a particular time. or I can run some script files.
But it does not seem sophisticated enough that I can call any function of a script (ie: perl). I need to call function because I need to pass parameters (entered by user via web interface)

Schedule::Cron does what I actually want. and I have a running code with cron.. but I want to run my scheduled jobs only once. this is the problem with cron.
so if I say $cron->add_entry("00 10 26 07 *") I want it to run at 10am, 26th of June 2004 but not at the same time of 2005.

I am not sure if this is the already case.. If so, not problem anymore

Nurcan