about chmod,
Problably you have a local server to simulate your scripts before upload them to the server. No matter if you use Apache under windows or IIS , a chmod instruction like chmod($filename,O777) may not work because windows does not handle that kind of permission's format.
So being in your local server, if you have a only read file and you try to erase, it will show that you dont have permissions even when you have already executed your chmod instrucction correctly. Just up the script it must work well in your internet server if it is a linux machine
fonte:
http://it.php.net/chmod

altre info su:
http://www.google.it/search?hl=it&q=...n+Google&meta=