I did manage to solve the problem - win2k
works slightly differently from winXP. After posting this thread i
found (hidden in some manuals) in the box that came with this PC the
recovery disks having all drivers etc. Once i had installed XP and
switched the cables back it worked fine. For me to use win2k i needed
to modify the boot.ini and i would have also had the pain of finding
the necessary drivers... so as i had XP it was better to install that.

This method of dualboot is excellent as it allows one to do an
independent install of either operating system. In my case ubuntu for
95% use and just switching occasionally to windows for a couple of
apps and using the scanner that came with it. I still find that i have
some DVDs that won't play on ubuntu and yet play on windows media
player (a wimbledon finals which i loved watching!).

The other advantage of this dualboot method (imo) is that ubuntu 6
month releases are easy to accommodate. One can change the file to
allow winXP to boot first if that is desired.