Hi
May be this can Help.
DialUp http://www.ezlan.net/DialUp.html
Optimizing the TCP/IP Stack - http://www.ezlan.net/Internet_Speed.html
Jack (MVP-Networking)

 it could be the MTU issue. quoted form http://www.howtonetworking.com/troubleshootingie.htm
Can't access some web sitesSymptoms: 1) If you're using MS ICS or Windows server as router to access the Internet, your clients may not be able to access certain web sites. However, the ICS host or the server doesn't have this problem.
 2) After installed a new router or cable modem replacing dial-up to access the Internet, you can't access some web sites.
 3) You also find that most web sites you can't access are block to ping or they are security sites using HTTPS.

 Causes: 1) The problem occurs because many web servers block ICMP messages and the packets are dropped. As a result, the requested web site doesn't load.
 2) This problem is caused also by an incompatible MTU networking setting. You may try to install the latest SP. If you use MS ICS, you may want to configure all your Client computers to use the new, lower MTU as the default for all Internet communication. To modify the MTU size, locate the following registry key: HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip\ Parameters\ Interfaces. If you use a router like Cisco DSL Router, you may want to adjusting the PPPoE MTU Size. For example, to adjusting the PPPoE MTU Size on the Cisco DSL Router, do

 interface ethernet0
  no shut
  ip address <ip address> <subnet mask>
  ip adjust-mss 1452

 Don't send e-mail or reply to me except you need consulting services. Posting on MS newsgroup will benefit all readers and you may get more help.

 Bob Lin, MS-MVP, MCSE & CNE
 How to Setup Windows, Network, Remote Access on http://www.HowToNetworking.com
 Networking, Internet, Routing, VPN Troubleshooting on http://www.ChicagoTech.net
 This posting is provided "AS IS" with no warranties.
 I recommend Brinkster for web hosting!

   "J. Murray" <jmurr@jisp.net> wrote in message news:p17521tgj3i2r0v9kmimn5v4tsqrkldgpd@4ax.com...
   I have recently replaced a Win2000 system on my home network with a
   Dell 2400 running WinXP Home w/sp2 as the client.  I have set up ICS
   for want of a better solution (I use a dial up ISP).  The trouble is
   with the client machine, I cannot connect to all web sites, only some.
   This was not the case with the old system, all was well with it.  I
   have also tried an old version of Sygate Sharing software I used with
   the Win2000 system but still no joy.   I can connect to
   www.google.com most of the time, sometime on the first try and
   www.dogpile.com but not to others like www.cnn.com or www.msn.com.
   I.e. displays "opening page. . ." on the bottom of the screen but then
   displays error "page cannot be displayed".  If I ping the addresses
   than can not be displayed they time out, the ones that can display of
   course return normally. I have turned off Windows firewall and
   suspect something is not working properly with the DNS on the client
   but am far from a computer guru so do not have a clue what to do next.
   Everything works as it should on the Gateway machine, I can connect to
   all sites.  Any help would be greatly appreciated.

   TIA

   Jim