Re: how to access a computer from a router?
(Assuming your running Windows 2k/XP)
Under your Local Area Connection Properties, set up "Client For Microsoft Networks, "File & Printer Sharing", & "TCP/IP". After all that is set up goto "My Network Places" and click on the "View Workgroup Computers" link. Then click on the unit you wish to connect to.
These are very basic instructions. I am assuming you covered all the other basics prior to doing the steps above (IE Naming and physical setup of router and cables)