The Windows share must be already shared (a restart of Windows after setting this up helps), and if you set a password for it you may have to try it a few times before it really works. You should also make sure you've set up Windows File Sharing on your BlackBook (Preferences, Sharing). BOTH are required for this to work.
Another issue that your post brings to mind is that the PC is getting its IP address dynamically. What you have set up seems to be an alias to a specific IP, rather than to a specific computer. Get Windows to tell you how its network card is set up (right-click on My Network Places and select Properties, then right-click on the network adapter and select Properties). If it says that it's getting a dynamic IP (through DHCP), then that's probably the issue, and you can get around this. Set up a NEW alias for just the computer name (not the IP), and save it to your server list.