Sikpupi,
Had to clean up a collegues PC who was riddled with various virus.
By the sounds of this, you should back his data up and do a fresh install of Win98 from the CABs. Many viruses are destructive and you might find in the end that the OS is trashed and a new install is required.
The problem with vielqsu.exe is that it was deleted and something either in the msconfig or in the registry is calling for that file. Since it is no longer on the computer it is giving you the error.
Run msconfig and see if the file is being called there. If it is, remove the check mark next to it. If it is not there, then do a search in the Registry. When you find it there, delete the DWord and/or Key.
Take Care,
Richard
P.S. I still think a fresh install is the way to go.