saving an image

I think I'm missing somethign here, basically what I'm trying todo is have a page where someone enters a url and the server will grab that image and save it locally on the server. now I can easily grab the pic and display it, but as soon as I goto write it, it doesn't. I just thougt of usig gd, but I want to try todo it with out it, so I can adapt the script for other file types. Has anybody done this in some way? if so can you send me code. I know I'm missing one stupid little thing too. Christopher Riordan