Internet Connection Sharing not working

Should be like this

Ethernet adapter Local Area Connection 4:

        Connection-specific DNS Suffix  . :
        IP Address. . . . . . . . . . . . : 192.168.1.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : (dont enter a default gateway)


XP Home Machine
Network Connection
Ethernet adapter Wireless Network Connection:
        Connection-specific DNS Suffix  . :
        IP Address. . . . . . . . . . . . : 192.168.1.101 (was conflicting with above same address)
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.100

Ensure you set your DNS on the XP Home Machine to your ISP's DNS
     Do a IPCONFIG /ALL on your Win XP Pro
    Check out the DNS listed from Ethernet adapter Local Area Connection:(the one connected to your Modem).  Write these down and enter them in DNS for your XP Home machine

Your IP addresses for the following are in conflict.  They should be unique addresses.

Ethernet adapter Local Area Connection 4:

        Connection-specific DNS Suffix  . :
        IP Address. . . . . . . . . . . . : 192.168.1.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1


XP Home Machine
Network Connection
Ethernet adapter Wireless Network Connection:
        Connection-specific DNS Suffix  . :
        IP Address. . . . . . . . . . . . : 192.168.1.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1

Again, the default ip scheme on XP with ICS can not be changed, it MUST be 192.168.0.1 (for the host LAN NIC)
here is the M$ KB on setting it up
http://support.microsoft.com/default.aspx?scid=kb;en-us;306126

and from
http://support.microsoft.com/default.aspx?scid=kb;en-us;314066

"Important When you enable Internet Connection Sharing, the network adapter that is connected to the home network or to the small-office network receives a new static IP address of 192.168.0.1, with a subnet mask of 255.255.255.0. Existing TCP/IP connections on the network may be lost and must be reestablished.
Configuration and usage issues
Internet Connection Sharing is intended for use in a small office or in a home office where the network configuration and the Internet connection are managed by the Windows XP-based computer where the shared connection resides. It is assumed that on this network, this computer is the only Internet connection, this computer is the only gateway to the Internet, and this computer sets up all internal network addresses. All hosts on the network except the Internet Connection Sharing host are expected to be configured to obtain an IP address and DNS configuration automatically.

You cannot modify the default network configuration after you enable Internet Connection Sharing. This includes changing the range of private IP addresses that are handed out (DHCP allocator), enabling DNS, disabling DNS, and configuring a range of public IP addresses."

Well It looks like I learned something today.  I never know that ICS had to have 192.168.0.1.  I though it could be any address as long as the 2 machines were in the same range.  Looke like you will have to change all the 192.168.100.X to 192.168.0.X.

Follow the instructions from stevenlewis's link.  They should be able to step you throught it.