If you right click in the box where you enter the name of the file to be saved, it comes up with a menu of the variables and includes the options for leading zeroes etc.
I use these for my archive files each day with "ddMMyyhhmmss" as the format... works perfectly...
Obviously once you know the name of the variable, you can type it in after that. The menu is a good option for finding out what they are though.
Thanks,
Andrew