Can someone give some pointers, please.

I want to write a web application that will allow me to synchronize the content of a folder
in my PC with a folder in my website/webhost.

Does anyone know how I can do this in the most simple way?
What language should I use? Do I need activeX?

The program should not need to be installed in the PC, so when I'm at a public PC (say,
at an Internet cafe) where I may not be able to install anything, I can still synchronize
my data.

Any help or ideas will be greatly appreciated.
Thanks.