I need more info on your network. Your IP schema is not the normal 192.168.1.x network which is ok but do you have more than one subnet on your network? Run IPCONFIG on your PC and let me know the IP address. If the PC is on a different subnet than the NAS drive that could easily be the problem.
I need more details to help you out. I own three of these 4100's and they work great and usually don't have any issues mapping drives with Windows.
Are you able to see the folder by typing \\\\192.168.2.105 at the start run prompt?
This is weird, so you can see the web interface from the XP PC. But that same PC cannot see the folder shares. You mentioned it prompts for a password trying to map a drive but at the command prompt you just get a network error which makes no sense.
Please post a screen image of your shares. (Storage, share folders). Also review your System Information, System log, maybe an error is being logged.
Also which port on the back is your network cable plugged into?
Do you have any other PC's to test with?
Also if you have not rebooted the NAS please do so. Anytime you add a share I found it sometimes is not registered until a reboot.