Disabling -ve DNS Caching (XP+)

Save the following as a .reg file and double click it to submit ro the registry.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters]
"ServiceDll"=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,\
 00,74,00,25,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,\
 64,00,6e,00,73,00,72,00,73,00,6c,00,76,00,72,00,2e,00,64,00,6c,00,6c,00,00,\
 00
"MaxCacheEntryTtlLimit "=dword:00000001
"NegativeCacheTime"=dword:00000000
"NetFailureCacheTime"=dword:00000000
"NegativeSOACacheTime"=dword:00000000

Alternatively the full instructions / explanation are here.