I have in the past installed Ubuntu on to a drive running XP
Quite painless operation and- when starting the machine in this configuration simply got a 'selector panel up asking me to select which system.- OK

This time around I have treated my to a new 1Tb drive and installed Ubuntu 10.10.
All runs well
When I got the XP disk to go through the motions- it detected 2 partitions and asked which to select, but would not install on either
Does this mean I will have to clear the disk and install XP first then Ubuntu or is there a work around?.

Simplest answer, yes.
Since Windows isn't aware of linux partitions, while linux IS aware of windows. It is best to install windows first, and allow the Linux installer to resize the partitions to make space for Linux. Particularly if you aren't comfortable with resizing filesystems, and partitions.

Alternatively, you can resize the filesystem (assuming you selected a FS that allows for down-sizing)
resize the largest partition, creating space for windows XP
Install windows XP into the free space.
Then recreate the grub configuration, to recognise both the windows and linux partitions, and reinstall grub to take over from the windows boot loader.

Its probably simpler to backup you data, install windows, then install linux. IMHO

Thanks
I guess that is what I will do-
Transfer the Linux files to external H/D then do as you suggested.
Thank you.