When making DNS changes, you want to make sure your change was successful and undoubtedly you want to start getting the new address that corresponds to your change. Sometimes, your computer won't pick up this change because the address has been cached. The reason is that DNS tells your computer that this information is good for a certain length of time, so don't bug me every time you want to find such-and-such host. That being the case, it may take many hours before your computer checks for updated information. Here's a way for you to force your computer to get the latest and greatest DNS info by flushing the dns cache.
On Windows:
Open a command prompt and type
ipconfig /flushdns
On Mac OSX:
Open a terminal session and type
lookupd -flushcache