What I have is a genuine version of XP but with no XP CD.
For info when I last tried to boot into RC it was from the CD image rc.iso - that is what resulted in the 'no hard disk drives' error.
The SourcePath registry setting was already set to C.
The sfc scan seemed to complete without any errors (I was away from the machine when it finished)
I looked at Computer Management and there are lots of errors and warnings dating from when my malware problems started (this month) Maybe you'd expect to see this.
I'm away from this machine for a few days now. Hope you're taking a break too!
Thanks again for your help