Networking to share files

Sorry for my constant annoying newb questions.

Downstairs, Windows 98 computer has the files I want to access. (host, is it called?)
Upstairs, Windows 2000 computer is where I want to access the files.

Both computers are already set up with a cable modem and a router (upstairs) and the downstairs has a d-link wireless USB adapter. It's been like this for over 2 years, but both computers aren't connected to each other in terms of file/printer sharing. I read the How Stuff Works article ( http://computer.howstuffworks.com/home-network4.htm ) and (for the downstairs, Win98 comp) named the computer and workgroup, and added the files I want shared to the workgroup. Now, how do I access the files from the upstairs computer? I can usually figure these out by myself, but upstairs when I click on the Network Neighborhood the DownstairsComp doesn't show up. What else do I need to do?

"The list of servers for this workgroup is not currently available." This is what I get from my laptop (networked with a wireless card) when I look under the downstairs computer's workgroup. What do I need to do?
 
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