Undo Windows98 Installation

Our PI computer is getting the Vmm.vxd error. I did read the answer to the question posed on 1/14/01 Receiving Continuous Vxd Vmm Errors. The problem now is we tried to reinstall windows98 and the system ran out of hard disk space during the system file extension process before any window98 file could be install. The system should have had enough space. How can we undo this process. I did create an undo disk at the time of installation.