I've tried both my ISP's regular DNS servers, as well as some other public OpenNIC DNS servers, and just today, certain well-known sites aren't resolving, while others (such as this BBS) are fine. Anyone else?

Examples of stuff that's not resolving for me:
www.microsoft.com
www.hotmail.com
www.dnsstuff.com

Stuff that resolves fine:
Google
Livejournal
This BBS
Blue's News

And if no one else is having this problem, then what could it be on my system that causes this? I've checked my HOSTS file and it's fine. I've got no spyware or viruses.
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Tony Fabris