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Hey, thanks everyone. J2, you're right' after I set the 2nd drive to slave (but had not reset the master yet) it wouldn't boot.
Yes, those jumper thingies were causing the trouble. Had the same problem 4 years ago when I added a CD-writer. Forgotten about that;-(
Had quite a bit of trouble setting the master HD though. Only 8 pins, but two jumpers. Nine combination on the label for master/slave/cable options, each for upper/lower/clpi(?). No clues on the Net. Samsung site was useless for support too. Anyway, I took the most likely looking option and it worked straight away.
The default C/drive[NTFS] has XP as was installed, with a 4GB locked partition as D/drive[FAT32], which has the XP recovery in it.
The F/drive[FAT32] is the one with my old HD and I seem to be able to easily transfer folders with piccies or documents between one and the other, despite the difference in file systems. I originally thought when accessing it, the installed OS (windows98) might start up, but no, it opens as a directory and works just like a gigantic floppy drive.
When I am eventually happy with XP, I'll re-format the extra drive and keep all my goodies on it for safety, that'll should be a lot quicker than having to write everything on CDs every month. Thanks again.