Millenium Edition Install w/out losing data

I am working on a customers PC and it has ME installed. I am familiar with ME but not with this issue.
It has an error that stops the boot process resulting from a iosubsystem driver error. I spent several hours on trying to alleviate the error by changing boot parameters but nothing has helped.
The question that I now have is whether it’s possible to re-install ME without losing the customers data? I have been reluctant to go past the setup screen relating to “windows will now copy setup files”.
Any help would be appreciated.
Thx, Gale