<input class="loginField" type="text" name="user" value="" size="20" style="width:100px" maxlength="25" />

<input class="login" type="text" name="user" value="" size="20" style="width:100px" maxlength="25" />

<input class="loginField" type="password" name="password" size="20" style="width:100px" maxlength="15" />

<input class="pass" type="password" name="password" size="20" style="width:100px" maxlength="15" />

input.pass  
{  
background: url(/images/pass.gif) no-repeat;  
background-color: #fff;  
background-position: 0 50%;  
color: #000;  
padding-left: 18px;  
}  

input.login  
{  
background: url(/images/login.gif) no-repeat;  
background-color: #fff;  
background-position: 0 50%;  
color: #000;  
padding-left: 18px;  
}

<script>  
document.all.user.className='login';  
document.all.password.className='pass';  
</script>