adding a 3rd computer

[bac0926]

I just bought a new computer I would like to be able to hook up the old one to
my router. (I currently have two computer hooked up to the router) how do I go about adding the 3rd computer. The router is a Linksys  four port router
the idea is that I can access the 3rd computer from either of the other two
2 computers are running Windows XP Pro the 3rd is running Ubuntu 8.04

[RubiK]

If the new computer is close enough to be connected to the router via. an Ethernet cable, do this.

Alternatively, is there a wireless card in the computer? If so, tell the computer to connect wireless.

RubiK

[soybean]

the idea is that I can access the 3rd computer from either of the other two
2 computers are running Windows XP Pro the 3rd is running Ubuntu 8.04

so, you want to network Windows and Ubuntu computers so that any of the 3 computers can see files on the other two, right?  I have Windows and Ubuntu systems but have not networked them for file sharing between Windows and Ubuntu.  All I can suggset is to do a Google search on networking windows and ubuntu and start researching it.