ASP,PHP doubts

Well i have a little proect going on.. I need to give access for the users to upload PHP and ASP files to he server... the server runs the HTML interface using ASP... So how do i do it.. The user can write harmfull stuff in the ASP and have the server run it while accessing it.... so any solutions.. and i dont know baout PHP.. if my server runs PHP and i give access to upload PHP files.. will the same problem arise...

have the people save the files as .phpx (.aspx) or something useless, then you can have the server rename them after saving so they don't execute when they're uploaded....
do you plan on manually checking them for malicious code? or are you trying to do that with the server?