Err, just to clarify, by "a script" I mean "a script on the webserver"...

If you want to upload a file to a server that you have, say, ftp access to, then it should be fairly straightforward. You should also be able to write a script that uploads a file to a website provided that you are running the script on your machine, not the website (using mechanise?)

What you cannot do is write a script, place it on a server, and have that script automatically upload a file when someone accesses it.