Windows XP Registry – Big Problem

My machine will not run the Registry using Windows XP and will not allow me to run things like chkdsk from the command prompt.
Looks like a major problem.
I can log on, the wallpaper appears and then nothing…
So, can I connect the machine to another machine to copy or back up the hard disk on the problem machine? I have been told that it’s better to remove the HDD and connect it separately. Any comments or thoughts on that?