'Ghost' devices can be caused to remain in Device Manager when devices such as netcards or CD-ROM / DVD drives are replaced without uninstalling the original device first. Before permanently removing any hardware, for example when upgrading, you should always:
Though undesirable, ghost devices are often not a particular problem, and most users remain unaware of them because normally they aren't visible in Device Manager. However, while other types of ghost device such as netcards can also cause problems, ghost CD-ROM / DVD drives seem to be more frequently a problem than any other type of device, probably more than all the other types of device added together.
A typical scenario is that someone upgrades a CD-ROM drive to a burner, or a CD-burner to a DVD-burner, by just physically removing the old drive and reconnecting the new one in its place. Then when the machine boots up, either the new drive is not detected, or it has a yellow exclamation mark in Device Manager signifying it has a problem, or everything appears normal in Device Manager, but the burning software doesn't interact with it in the expected manner.
The cure for all types of device is to remove all the old ghost devices and the new device and then reboot to let the new device be redetected properly. Unless there is also some other problem such as a shortage of system resources like DMA or IRQs, this procedure will normally work.
In W9x (here my memory is a little hazy as I haven't worked with W9x for a while):