One computer can 'see' the other, but not vice versa

I have two computers on a wireless network at my home. One is running
Windows 2000 (downstairs) and the other Windows XP Professional
(upstairs).

Recently I replaced my router and I've been having trouble getting the
computers to 'see' each other. This is a router that I've used
successfully in the past so I don't think it's the router hardware.

Currently the problem is that the upstairs computer can not access a
share on the downstairs computer.

This is odd because the downstairs computer can access a share on the
upstairs computer.

Here are some clues

+ Both computers can access the internet
+ I can ping both computers from each other.
+ Both computers are on the same workgroup
+ I'm not specifying a domain
+ Both machines have the same subnet mask
+ I've attempted this with my firewall software both on and off but
with no change in results.

Any clues on what to check? I have more information to provide but
didn't want to overwhelm.

 

Hi
This is strange, as far as LAN traffic is concerned the Router is a dumb
switch.
May be that the IP scheme is different, i.e., the IP numbers of the
computers is not of the same range. If you have Software Firewall or any
other application that is based on IP numbers (trusted zone), check it, and
update the IP numbers.
May be this can Help, http://www.ezlan.net/sharing.html
Jack (MVP-Networking).

 

This screams out that there is a software firewall *somewhere* blocking the
connection. That said, it is possible that there is a peculiar hardware fault