Hi hardik,
You can see the Buffalo unit in the Nas Navigator and that means you are able to see the IP address and firmware information. Check the IP address and then set a static IP on yout Vista computer to match the same address range of the Buffalo unit. eg: Linkstation's Ip is 192.168.1.100, you should set your computer's Ip address to 192.168.1.123.
Pls make sure yout Windows defender or any other firewalls are switched off temporarily when performing this task.
Pls double-check when you run Nas Navigator, is the Link LED on the Linkstation flickering.