The default subsystem provided by Ulteo is an Ubuntu Lucid 32-bit. This page explains how to create an OVD subsytem in Debian Squeeze 64-bit.
An OVD subsystem is basically a chroot with some extra packages to provide Ulteo OVD functionalities. Ulteo provides packages for Ubuntu Lucid and Precise, and Debian Squeeze. For Debian Wheezy, some packages are missing (mainly uxda-server) that prevent to install a subsystem based on Debian Wheezy. See http://archive.ulteo.com/ovd/4.0/ for available operating systems packages.