Technical Requirements

There shouldn't be any requirements that any web hoster wouldn't comply with, but here they are:

PHP 5.3+
PHP PEAR (to install on Debian/Ubunto, run apt-get install php-pear).
Read/write permissions on your webspace
Reasonable amount of protection, i.e. only authorised users (you) can upload/download the files
Ideally with it's own IP address (makes configuring the VPN easier)