Microsoft Knowledge Base Article 318803 contains the following summary:

Windows contains a client-side Domain Name System (DNS) cache. The client-side DNS caching feature may generate a false impression that DNS "round robin" is not occurring from the DNS server to the Windows client computer. When you use the ping command to search for the same A-record domain name, the client may use the same IP address. This behavior is different from Microsoft operating systems earlier than Windows 2000. These operating systems do not include the client-side DNS caching feature. This article describes how to disable DNS caching.

Note This article refers to the client portion of DNS. Do not use this information for making changes to DNS servers.