To help stop problems like these, use
OPEN DNS. It's a free DNS server which is HUGE, and most likely faster than your ISP's own servers (massively faster if you're on VM cable lol).
They're secure, reliable, and free. You can even sign up for a free account which allows you (and only you) to track domain request stats, and gives you white and black lists for what sites your network is/isn't allowed to access. You don't have to sign up to use them however, that's just an optional extra. They have built-in phishing protection too! It's a great service.
Their site gives full details on how to change your DNS servers, either on the router (which will mean all PCs use OpenDNS) or just on individual PCs (including instructions for Vista). Give them a go and see if it sorts the issue you're having.
