dns setting question

I have a Linksys WRT54G Router.
The adapter is a standard Linksys b adapter.
There was good signal strength with an ip assigned.
However web browsing was not possible.
Turning on the dns server in the network settings in the computer
(Windows 98) solved the problem and allowed web browsing.
Several hours later web browsing was not possible again.
By turning off the DNS setting web browsing was restored.
Nothing was changed in the router.
Could someone please explain this to me >

thank you