That sounds like a strange problem. I never had problems like that geting windows XP onto my tecra 8100 using an authentic cd nor a copy of my authentic cd. Nor did I have problems getting non-authentic copies of 2k on there. Is the CD ok? Have you tried using the cd in a different machine? Maybe your cdrom is not reading properly.
To see if it's the cd disc, pop it into a desktop or other pc and see if you can copy the contents of the cd (at least the contents of the i386 folder) into a folder somewhere on the harddrive of that pc (not installing it, just copy it, and make sure to put it in a new folder becasue if you copy over the i386 folder that's already in c on that pc, you may end up with a big mess). If it comes up with any errors, then you can assure that the cd is screwed and you'll need a differnt disk. If ther are no errors, then the cd should be ok and it may either be a problem with the cd drive or the harddrive (have you run scandisk and done a surface scan of the harddrive?).