Could be the hosts file  as DeXter says ... anyway on windows 98 the hosts file if present will be at C:\Windows and C:\WINNT\SYSTEM32\DRIVERS\ETC for Win 2k ...
If nothing works post your HijackThis logfile - http://www.spychecker.com/program/hijackthis.html
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Hardware - Celeron 266 MHz, 128MB RAM, Intel i740 8MB RAM
Software - Slackware Linux 10.1; Archlinux 0.7; Windows 98 SE
Humanware - GS/CS C++ L+++ w b+++ DI+ D+ e
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