For a great 5 min introduction to how DNS works, check this:
http://www.youtube.com/watch?v=72snZctF ... re=channel
At the moment, when you click a link or open a web page, your computer needs to find out the IP address of the server where that page resides. So a web address like '
www.powerswitch.com'
resolves to the IP address 213.229.84.195
First, your browser has a look in it's own cache, to see if it has it already (because you've recently visited that page).
If it's not in the cache, the browser asks the Operating System (windows, ubuntu, etc) where to look it up. This is the setting in generally stored in 'network properties'. By default, the OS is usually configured to get this automatically from the internet 'gateway' (in your case, the router). This can be overridden by putting in the DNS server IP addresses I gave above, forcing the OS to go straight to that server, bypassing the router's and your ISP's DNS.
If set to look to the router for the DNS server address, it will ask the router, which will then go to the DNS server address that's buried somewhere in the settings of the router. This will usually be the IP address of your ISP's own DNS server, and again, would have probably been set automatically (or already set by the ISP if they sent you the router).
Their are two DNS server IP addresses set (primary and secondary) to give you redundancy should the first one of them 'fall over'.
Sometimes, if your ISP's DNS servers are under a heavy load or whatever, you'll fail to get the IP address - hence a 'DNS Error'.
So I'd probably leave the router set as it is, and change the DNS addresses in the OS.
To do this in WindowsXP (assuming that's what you use), go to 'network properties' > 'connection properties' (right click on the connection you use) > Highlight 'Internet Protocol (TCP/IP)' and click 'properties', then set the DNS server from 'Obtain DNS server address automatically' to '..manually' and enter the numbers and hit 'ok'. Then restart the computer. If it's currently set to 'automatically' obtain DNS settings, that's all you need to 'revert' to if you wish to undo what you did.