If you want to install Magento on WAMp server, localhost,
then you are going to face a very irritating problem with it,
which doesnt let you go into the admin panel, even if you enter the correct details. Ok,
here is the simple fix to override this problem.
Open this file, app/code/core/Mage/Core/Model/Session/Abstract/Varien.php and find
the session_set_cookie_params(line-78) and replace your code with this

{chilicode php content}   session_set_cookie_params(
    $this->getCookie()->getLifetime(),
    $this->getCookie()->getPath()
    //$this->getCookie()->getDomain(),
    //$this->getCookie()->isSecure(),
    //$this->getCookie()->getHttponly() 

 

);

{/chilicode}

 

Update (For Magento 1.4.*)

In Magento 1.4, you have to comment code from line 86 to 98 in app/code/core/Mage/Core/Model/Session/Abstract/Varien.php. Like this:-

 {chilicode php content}

 

/*  if (!$cookieParams['httponly']) {
	unset($cookieParams['httponly']);
	if (!$cookieParams['secure']) {
		unset($cookieParams['secure']);
		if (!$cookieParams['domain']) {
			unset($cookieParams['domain']);
		}
	}
} 

if (isset($cookieParams['domain'])) {
	$cookieParams['domain'] = $cookie->getDomain();
} */

{/chilicode}

 another way to access the admin panel just simple change in your url use 127.0.0.1 instead of localhost