How Can I Create A Login/Registration Pop-Up Or Lightbox In Dreamweaver.

It is not require Dreamweaver, It is the part of coding.
You can develop popup in any editor.
Here I try to create login popup. May it will help you.

Here is the code for you.
HTML

<div class="main">
    <div class="panel">
        <a href="#login_form" id="login_pop">Log In</a>
    </div>
</div>
<!-- popup form #1 -->
<a href="#x" class="overlay" id="login_form"></a>
   <div class="popup">
     <h2>Welcome Guest!</h2>
     <p>Please enter your login and password here</p>
   <div>
   <label for="login">Login</label>
   <input type="text" id="login" value="" />
   </div>
   <div>
   <label for="password">Password</label>
   <input type="password" id="password" value="" />
   </div>
   <input type="button" value="Log In" />
   <a class="close" href="#close"></a>
</div>

CSS

.main {
    background: #aaa url(../images/bg.jpg) no-repeat;
    width: 800px;
    height: 600px;
    margin: 50px auto;
}
.panel {
    background-color: #444;
    height: 34px;
    padding: 10px;
}
.panel a#login_pop, .panel a#join_pop {
    border: 2px solid #aaa;
    color: #fff;
    display: block;
    float: right;
    margin-right: 10px;
    padding: 5px 10px;
    text-decoration: none;
    text-shadow: 1px 1px #000;

    -webkit-border-radius: 10px;
    -moz-border-radius: 10px;
    -ms-border-radius: 10px;
    -o-border-radius: 10px;
    border-radius: 10px;
}
a#login_pop:hover, a#join_pop:hover {
    border-color: #eee;
}
.overlay {
    background-color: rgba(0, 0, 0, 0.6);
    bottom: 0;
    cursor: default;
    left: 0;
    opacity: 0;
    position: fixed;
    right: 0;
    top: 0;
    visibility: hidden;
    z-index: 1;

    -webkit-transition: opacity .5s;
    -moz-transition: opacity .5s;
    -ms-transition: opacity .5s;
    -o-transition: opacity .5s;
    transition: opacity .5s;
}
.overlay:target {
    visibility: visible;
    opacity: 1;
}
.popup {
    background-color: #fff;
    border: 3px solid #fff;
    display: inline-block;
    left: 50%;
    opacity: 0;
    padding: 15px;
    position: fixed;
    text-align: justify;
    top: 40%;
    visibility: hidden;
    z-index: 10;

    -webkit-transform: translate(-50%, -50%);
    -moz-transform: translate(-50%, -50%);
    -ms-transform: translate(-50%, -50%);
    -o-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);

    -webkit-border-radius: 10px;
    -moz-border-radius: 10px;
    -ms-border-radius: 10px;
    -o-border-radius: 10px;
    border-radius: 10px;

    -webkit-box-shadow: 0 1px 1px 2px rgba(0, 0, 0, 0.4) inset;
    -moz-box-shadow: 0 1px 1px 2px rgba(0, 0, 0, 0.4) inset;
    -ms-box-shadow: 0 1px 1px 2px rgba(0, 0, 0, 0.4) inset;
    -o-box-shadow: 0 1px 1px 2px rgba(0, 0, 0, 0.4) inset;
    box-shadow: 0 1px 1px 2px rgba(0, 0, 0, 0.4) inset;

    -webkit-transition: opacity .5s, top .5s;
    -moz-transition: opacity .5s, top .5s;
    -ms-transition: opacity .5s, top .5s;
    -o-transition: opacity .5s, top .5s;
    transition: opacity .5s, top .5s;
}
.overlay:target+.popup {
    top: 50%;
    opacity: 1;
    visibility: visible;
}
.close {
    background-color: rgba(0, 0, 0, 0.8);
    height: 30px;
    line-height: 30px;
    position: absolute;
    right: 0;
    text-align: center;
    text-decoration: none;
    top: -15px;
    width: 30px;

    -webkit-border-radius: 15px;
    -moz-border-radius: 15px;
    -ms-border-radius: 15px;
    -o-border-radius: 15px;
    border-radius: 15px;
}
.close:before {
    color: rgba(255, 255, 255, 0.9);
    content: "X";
    font-size: 24px;
    text-shadow: 0 -1px rgba(0, 0, 0, 0.9);
}
.close:hover {
    background-color: rgba(64, 128, 128, 0.8);
}
.popup p, .popup div {
    margin-bottom: 10px;
}
.popup label {
    display: inline-block;
    text-align: left;
    width: 120px;
}
.popup input[type="text"], .popup input[type="password"] {
    border: 1px solid;
    border-color: #999 #ccc #ccc;
    margin: 0;
    padding: 2px;

    -webkit-border-radius: 2px;
    -moz-border-radius: 2px;
    -ms-border-radius: 2px;
    -o-border-radius: 2px;
    border-radius: 2px;
}
.popup input[type="text"]:hover, .popup input[type="password"]:hover {
    border-color: #555 #888 #888;
}

Demo link

http://codepen.io/ashishbhatt/pen/JbdDl[^]