Not familiar with Comcast.
They may use static IP's or may use DHCP to randomly assign them.
Your best bet is to phone tech support at Comcast and ask them how to deal with this issue.
To check if your IP is hard coded in your TCP/IP network settings in WinXP:
Start / Control Panel / Network Settings / Properties
click on: TCP/IP / Properties.
if it says:
"Use the following IP.." then it's been entered into your machine
if it says:
"Obtain an address..." then it calls out for an IP address from Comcast's server.
For the latter scenario, you can attempt to fix it by:
Start / Run / at the "open" line, type: cmd and hit the "ok" box. This will bring up a DOS box.
At the command line, type:
ipconfig /release
That will release the current IP address from your TCP/IP settings.
At the command line, type:
ipconfig /renew
That will request a new IP address from the Comcast server, if they are setup in that manner.
Again, your best bet is to call Comcast tech support so they can walk you through the above and ensure your machine is setup properly according to their requirements.
Regards,