So the disc arrived - thanks Xara - and I uninstalled my download copy of XDP X. Started to reinstall from disc and that's when the fun started. Setup routine seemed to run and complete smoothly, but then on starting XDP I got stuck at the splash screen. I gave it 3 minutes or so after which no indication of anything going on, no hard disk light. Uninstalled and tried again - this time remembering that sometimes "run as administrator" cures hiccups like this. Used this trick on both the installation routine and the first attempt at starting the program. This time, gets as far as the registration confirmation screen but then freezes. Uninstalled again, rebooted the PC, tried a third time to install and now everything goes smoothly, registration completes and - hooray - I'm back into a working copy of XDP. Nip over here to TG expecting to see one or two messages telling of similar problems, but haven't found one yet.
So why post? Well, I can't fathom why any of this happened but the moral is not to give up, because I got there in the end although I haven't a clue why the earlier attempts to install failed. Didn't touch any firewall settings or anything else. Used "custom" install but accepted the default settings it offered. BTW all this is under Windows 7 Home Premium 64-bit.