Magento

Hi, i need for Magento to keep the original filename of the attachments that I upload, and if it already exists overwrite the old file.

Even better would be if it was possible for me to parse file name, and create my own url structure.
So I guess that am asking if there is a way to hook into the whey way magneto handels attachment uploads without editing core files?

I am completely new to magento so all help is deeply appreciated!
/R