Check Windows Firewall and make sure it's allowing file sharing or is turned off. Do you have Norton Internet Security or McAfee? You don't really need a software firewall if you have a hardware solution in place. Kill the Norton firewall.

I've never had problems with a Linksys router not allowing file sharing. Typically it's something to do with software on the computers themselves.

I always love it when you buy a new pc and by default it can't connect to a server because of the stupid security software that comes pre-installed on them.

Did you share the specific folder(s) that you want access to?

Here are some helpful networking tools. The first one is mainly for wireless. The second one will give you information on what IP address' are at what hardware.

[Link: netstumbler.com]

[Link: snapfiles.com]