process forking?

Hi All, I've written a digital asset management system and my dilema is, to save a file from the sytem, i pass the files through a php script so i can change file names and keep the files out of the web tree. I use a little popup window so they can select what format they want to download the file as, but the problem is when downloading a file it seems to halt the rest of the site from being able to do anything until the download is complete. so i'm just trying to get the rest of the site to function while the download is in process, thank in advance. S.