Hi
Can you make the printers re-appear by refreshing the view (F5)?
There is a command in Windows 98 called SFC. Type SFC in the Run dialog box, then start the program. It will offer to replace any corrupt or missing core system files. You will need the Windows installation disc or be able to tell SFC where the CAB files are if any files need to be replaced. If the CAB files have been copied to your hard drive they are usually copied to C:\Windows\Options\CABS. Your issue may be solved by doing this.
Also make sure you have the latest versions of each of the drivers for your system. Presumably you connect to these printers over the network - you should also make sure that the machines hosting them are correctly setup and that the shares have been properly setup.
With regards to your last comment about whether this is a patch issue, I don't think there are any patches issued by MS which can cause this behaviour.
Good luck