If you changed a DNS zone (for example, an IP address), or you know that the DNS zone has changed, but that address still pings on the old IP for you - obviously, the address hasn't yet outlived its TTL and is still living in the cache of the Windows network system.
You can reset the entire cache. There's nothing wrong with doing so - it's constantly refreshed anyway and gets reset on reboot.
To do this, in the command prompt (on Windows Vista/7/2008 - run it as administrator) type the following command:
C:> ipconfig /flushdns
And the DNS cache on this machine will be reset.
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