Not exactly solved it. The Dell is a really smart piece of kit. It has in internal HDD, a hot swap internal drive bay, and you can get an external caddy (USB). The best bit is if you it F12 when the machine boots it gives you a one time boot menu, and you can say for this boot only I want to boot from external USB or internal hot swap, external CD etc. Very useful.
Mandrake would not boot when the HDD was in the external caddy. It does start to though. I get the Lilo menu (which is loaded from the external HD), and it does start loading. It is after about 5 - 10 secs I get the error. But being complete shite on Linix I dont have the skill to work around this, so my solution was...
Have internal HDD with XP. Have second disk and plug it into internal media bay, and put my CD in the external caddy. This is not really what I wanted, as I wanted internal XP, internal CD and External HD in caddy as I have two other drives and wanted one as Mandrake and one as win2k server. Anyway, after all the waffle mandrake boots fine in the internal Media bay and I can boot between the two drives using the F12 bios menu.
That was the long answer. Short answer is...... no.
Hope you get some success !!