Though I used the brute force method.
If you use HyperVM to administrate your Xen domu's there is an issue with the osteplate (at least for Debian) this also goes for the Debian image from jailtime.org. (though I am not sure about other distros), that prevents ftp from working when ISPConfig 3 is installed.
In order to get ISPConfig 3 working as a domu using HyperVM I had to install a xen dom0 on an old server, then create a basic debian domu with ssh installed. Then convert the domu image to a formate that HyperVM uses (debian-5.0-i386-minimal.tar.gz) then move this to the xen ostemplates of the HyperVM server. I was then able to use this template for building the ISPConfig 3 server, and all worked perfectly.
Many thanks to all involved while trying to fix this.