how to network new linux ubuntu 7.04 to existing xp computer with internet connection

I have a Pentium 4 dual core computer with windows xp installed connected to the internet with a adsl modem and ethernet cable .

I have just purchased a new (secondhand) Pentium D computer which also came with a wireless card to be used in another room and have just installed linux ubuntu 7.04 on that computer .

I would like to network the two and and be able to access files from each computer and to also to be able to have access to the internet on the linux computer through the existing xp computer internet connection.

Is this possible and if so what hardware would i need and is it difficult to set up the network on both computers. (I have decent basic computer knowledge but no networking knowlege or experience and I have not previously used Ubuntu).

I'm guessing if I wanted to connect by cable I would need an ethernet cable to conect from the linux computers ethernet connection and a new card (lan or networking is it called) installed in my xp computer which currently has the modem connected to it to be able to connect the cable to?

Otherwise would I be able to buy a wireless card for my xp computer and connect them wirelessly? - I have no wireless knowledge or experience also.

In both cases I have no idea as to what steps or settings I would need to complete to on either operating system or computer.

If anyone can offer advice I will really appreciate your time and help.

Thanks