I am also in the same predicament. I am running Retrospect Workgroup 5.6 on an XP Pro workstation. I backup to a USB device. My Windows NT server does not support the device, so I cannot run Retrospect from there. I am disappointed...I had upgraded from Desktop to Workgroup for this sole reason...Dantz's site says: "Retrospect Workgroup Backup effortlessly protects files on any local server plus 20 networked desktops and notebooks. Install Retrospect on your Windows NT® or 2000 Server or any other Windows PC along with a storage device." This is very misleading...this tells me the software will run from any machine and support one local server.
I can only hope Dantz changes there position on this immediately and fixes this for their customers...it is a very competitive market and I can think of many others vendors who will help me out.