Hello bern_81;
Are you trying to copy files to the SIM card storage or is there a MicroSD card in the phone as well? Does your phone require you to load any software (or driver) on the PC? Some do - some don't.
Usually, when hooked up via USB you see the phone as a new removeable drive on the computer and can view it's folders, create new folders, and copy files just like any other drive, or USB flash drive.