troubleshooing user.exe

we have win95/98 client nodes
since two days there are many pcs showing a common error page fault in module user.exe or iexplore has a problem in user.exe while accesing excel,word,notes,printing and many other applications.I tried searching on netbut no use.
i suspect nimda virus but no sign of it on the pc.may be after effect .
Anybody having solution pl help out asap.