Evidently the explorer.exe is corupted, try running the system file checker ( sfc ) utility to extract another one from the 98 install cd.
if this doesn't work, yo may have a coruppted 98 CD, so you can get a copy of the explorer.exe from a known working system.
Did you do a clean install? If not-then this may be the action of a Virus and by just reinstalling all you did was reinfect the system file. If this person doesn't have a antivirus program, you can get AVG for free and create a rescue disk-which you can use on their system to scan for virii.
If there are no infections, then i would suggest a clean wipe of the harddrive, then do a fresh window's install.
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iisbob
Computer-Show me the Enterprise; no bloody A, no bloody B, and no bloody C-just the original...Mr Scott { from a STNG episode }
iisbob
Read in a message board of a local BBS: "I try to avoid using Microsoft. That's why I use MS-DOS."