Using a computer as a "midway router"

Clarifications

Connection feature of XP Pro. I'm not sure XP Home offers that option, and since you haven't specified Home/Pro, that is another possible problem.

More data needed about the various settings tried to provide more (useful) guesses.

Good luck.

setup the second computer as a fileserver, and you can use it
similar to a hub. Install as many ethernet cards in it, and
also set it up to save all your files, incase any of your
computers crash. I think that's kind of what you are trying
to do. Download apache and read the instructions, unless
you have a copy of ubuntu and install it as a fileserver.You
do need a crossover cable to hook them together, or put a
hub first, then plug all the computers into that.

Is it not just as simple as setting up internet connection sharing.

Basically you will share the internet connection (out to the wired computer) which is being recieved through your wireless network adapter. Use a standard network cable (straight through) to connect dual boot machine to the XP machine.

To set up internet connection sharing:

Open control panel.
Open Network connections
On the left of the screen, under Network tasks, click "set up a home or small office network" ***see below***

Follow the instructions on screen.
Once complete you may wish to disable/turn off the windows firewall on the connection.

***
If you dont see this option, then click on "Tools" , "Folder Options", under the general tab select the option "Show common task in folders" radial button and then click "OK"
***

are all the client machines xp pro? try going cable modem - router - lan cable from router to desktop. add wireless usb or wireless card to desktop and then have your laptops connect through the desktop..make sure you disable the wireless in the router. but what is the desired out come? or reason to do this?