Great information. The next thing that I would do is a ping test.
1) Click on start | run then type cmd then click ok
2) Type ping 192.168.0.100 then press enter (replace with the correct IP for the machine opposite of the one you are using)
If the ping responds with packets, then either your firewall (on your windows machine) or your router is blocking the request.
Also try running the command "\\192.168.0.100" in your run line and see what happens (of course replace with the correct IP for the machine opposite of the one you are using)
In some cases your Antivirus software will replace your windows firewall (i.e. Norton Systems Works). You will need to disable the antivirus software firewall settings, not the windows ones if this is the case.
In response to your question above, if you are using windows XP SP2 or higher then you have this option. If you are not in SP2, then you will not have this option. If you are in the category view of Windows XP, then you want to choose "Security Center". If you are in the classic view, then you want to choose "windows firewall".
Like I mentioned before, your router could also be blocking this communication. In a web browser, navigate to "http://192.168.0.1" (this is the default admin page for d-link routers I beleive). Also the default login is admin and there is a blank password.