vpn problem

When I try to install the DUN1.4 upgrade - needed, I gather, to use VPN on
Windows 98, I get the error message

"This update is nor designed for your version of windows"

When I attempt a VPN connection to my work server, it seems as tho' I am
trying to connect using a modem, rather than via our router and cable modem.
Works fine on our XP machine, but clearly something is missing here

TIA
Jeremy Poynton