Outlook hangs, W2K upgrade, vpn, Win9x clients

[Guest_imported]

I have been having the following problem:

VPN server was working fine for all clients. Then I upgraded the PDC and two other domain controllers to Windows 2000 w/Active Directory. After the upgrade, everything was fine with one exception: Windows 9X clients accessing the VPN server over a DSL line could connect (e.g. map drives, browse) but when they tried to open Outlook to connect to the Exchange server Outlook locks up. If the same Windows 9X clients access the VPN server via dial-up connection to the Internet instead of DSL, everything works. All Windows 2K client machines connect fine.


Environment:
PIX firewall
Exchange 5.5 on Win2K member server - on dmz
3 Win2K domain controllers on lan, not dmz
1 NT4 domain controller on lan, not dmz
separate vpn member server on lan, not dmz
Ports open between Exchange and all domain controllers (dmz to lan):
UDP:
42
53
88
135
137
138
139
389
445
1025 (statically mapped TCP/IP Port of all domain controllers)
1512

TCP:
42
53
88
123
135
137
139
389
445
636
1025 (statically mapped TCP/IP Port of all domain controllers)
1512
3268
3269

VPN server has these ports open thru the firewall:
tcp: 135, 1723
udp: 137, 138
protocol port: 47


all clients connect thru vpn server and can map drives to lan resources
all w2k clients can also use outlook and exchange via pptp connection
W9x clients can connect via MODEM to ISP and then via pptp and use outlook and

exchange
w9x can connect via fast (e.g. DSL) connection, map drives but outlook hangs

w9x clients used to be able to use outlook via DSL and vpn/pptp but that changed

when I brought up three Windows 2000 domain controllers.