How to upload files

Hi all, I'm looking for a method to enable my users to upload thier html files and embedded pictures to my server. I think it should be something very easy, but as I'm doing it for the first time, I thought it would be better to seek help from the experienced one. So any idea, how can I do it easly and safely and what are the precautions I should take to check the files for valid HTML and pic files, so that they cann't upload any thing destructive. Any help or suggestions will be highly appreciated. Thanks in advance Nitin