Hi,
If you know the exact names of the files to be removed you can use the "New File Removal" toolbar option from the "Files and Folders" tab.
If you want to erase an random number of files in a folder or the whole folder you have to use a custom action. I would suggest a small executable to erase a folder given in the command line or some script. VBScript it is fairly easy to use for this purpose.
You can check out this URL for a sample of a VB script that deletes some files and folders:
http://support.microsoft.com/default.as ... -us;197425
Regards,
Mihai