Thanks but I had attempted that in the first instance, hoping the installer
would offer to use the original 200MB unallocated space behind my 'C'
partition.
But it only gave me the choice of sharing the XP partition or the Advanced
option in which I had at the time then formatted the 200GB for Linux &
directed it there.
It then asked for a mount point & I imagine I would also then have to
manually set up the required partitions & dual-boot system...all new
territory for a beginner where I could easily lose the ability to dual-boot
XP in the process.