check upload files (in realtime?)

Hi, My problem is that very often users who opens an account on my server for getting free webspace/free hosting (like on tripod or lycos or other services) they upload xxx videos or mp3 files and offer this to download. The result is that I have heavy load on my free servers, what I don't want of course. Now I search a way for checking the uploaded files for unwanted filetypes. Do you see a possibility for doing this in realtime? For example php seems to have new functions for handling with filestreams etc. Is there some way for checking that filestream to see what type of files the user is uploading with the upload-formular..? Do you see other solutions for my problem? Please do not posts standard bids or posts. Only bid/post if you really see some solution and can contribute to this problem. Thanks. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Installation package that will install the software (in ready-to-run condition) on the platform(s) specified in this bid request. 3) Complete ownership and distribution copyrights to all work purchased. ## Platform win/unix/linux