Cannot access intranet web servers via Win98 VPN client

This problem occurs with Win 98SE, upgraded to DUN 1.4, connecting to a
company VPN via a modem dialup Internet connection, and using IE 5.00
SP1 as browser. AWin XP Pro system with virtually identical VPN settings
works fine. One intranet server is Netware, other is Win2K. Everything
uses TCP/IP only.

The Win 98 system gives stable VPN connections, logs onto our Netware
LAN via the VPN and works fine with Groupwise Remote updates over the
VPN. I can ping both intranet servers by name over the VPN. I can also
use the intranet web pages ok from the Win98 system when connected
directly to the LAN at work or via a peer-to-peer link with the WinXP
system at home (I enabled ICS on its VPN connection).

I have tried setting Use Default Gateway for the VPN (not needed on XP
system) but the problem occurs even when Route Print shows the VPN
gateway as the top entry with metric 1.

Grateful for any suggestions re cause/fix.
MikeS