Well it sounds like you are hooked up something like this
In this case all of your computers "live" on the internet.
Your ISP is assigning IP's to your Internet connected computer and you may either be obtaining additional addresses or typing them in.
In the latter case, the addresses you "type in" are invalid because your machines "Live" on the ISP's "subnet".
This means any IP you choose may be already taken by someone else.
If you switch to Private IP's you'll have problems with the internet connection.
You could set up your Xbox and PC directly like this.
and use PRIVATE Ip's as per the tutorial. This would give you pretty good speeds.
This requires two lan cards in your PC (but this has it's own problems, such as IRQ sharing, etc...)
The best way to do this is with a DSL/CABLE sharing device that has an integrated switch/hub
In place of 10-100 "router" substitute something like one of these...
http://www.dlink.com...wireless/di764/Everything would look like the diagram above, but would work at full speed. Each PC and the Xbox would be "given" an address by the sharing device which does not conflict with internet IP's.
The all-in one devices take care of all the settings for your lan automatically via something called DHCP.
All of the devices would have internet access, and you would not have to pay additional for this. As far as the ISP is concerned you have only one internet connected device, the Dlink.
With a direct cable connection or the latter setup you should see speeds in excess of 3,000kbps, making the transfers painless.
Others who have complained about exactly the same thing you have, later found out that their setup was at fault and once they "isolated" the cable modem from the LAN or used a sharing device, speeds increased greatly...
