Hi SJA, usually that message for the "missing command interpreter" is an ominous sign that there is irrepairable damage to the file system or partition information on the drive. If you were to do a site search here for the key words "command interpreter" I don't think you'd even find a fix.
However, there just may be some hope in your case. The other parts of the error message indicate that at least there is some partial success in reading the drive.
If you have a startup disk for the installed operating system, boot with it and at the a:\> prompt enter:
sys c:
You should get a message that "system files" have been transfered.
These will include the ones mentioned in the error message -- except config.sys.
Remove the startup disk and ctrl-alt-del to restart Windows.
If you can't get past the config.sys error, restart and hold the ctrl key down until you see the boot menu. Try selecting safe mode. If you can successfully start in safe mode, go to start, run msconfig and uncheck config.sys on the general page. Let us know what happens.
http://www.computerhope.com/issues/ch000012.htm
If you don't have a boot disk, you can create one from add/remove programs on a computer with the same Windows versions, or you can download a file which will create one from
www.bootdisk.com
see also:
http://www.computerhope.com/syshlp.htm