nav ul{
  list-style-type: none;
  padding: 15px 0px 32px 0px;
}

nav ul ul{
  display: none;
}


nav ul li{
  display: inline;
  float: left;
}

nav ul a{
  color:#666;
  background-color:#CCC;
  text-align: center;
  text-decoration: none;
  padding: 20px 20px 20px 20px;
  font-family:Arial, Helvetica, sans-serif;
}

nav ul a: hover{
  color: #FFF;
  background-color: #F60;
}

<nav>

    <ul>
    <li><a href="index.html">HOME</a></li>
    <li><a href="products_and_services.html">PRODUCTS & SERVICES</a></li>
        <ul>
            <li><a href="">BROCHURES</a></li>
            <li><a href="">BUSINESS CARDS</a></li>
            <li><a href="">MAGAZINES</a></li>
            <li><a href="">BOOKS</a></li>
            <li><a href="">WEB DESIGN</a></li>
        </ul>
    <li><a href="gallery.html">GALLERY</a></li>
    <li><a href="support.html">SUPPORT</a></li>
    <li><a href="contact_us.html">CONTACT US</a></li>
    <li><a href="about_us.html">ABOUT US</a></li>
    </ul>

</nav>

<nav>
<ul>
<li>Test</li>
<li>Test 2</li>
<li>Test 3</li>
</ul>

</nav>

nav {position:relative; top:50px; margin-left:auto; margin-right:auto; width:1024px; height:50px; background-color:#cdcdcd;}

nav ul {display:block; list-style-type:none; text-align:center;}

nav ul li {display:inline-block; margin-left:15px; margin-right:15px;}

<nav>
<ul>
<li><a href="index.html">HOME</a></li>
<li>
    <a href="products_and_services.html">PRODUCTS & SERVICES</a>
    <ul>
        <li><a href="">BROCHURES</a></li>
        <li><a href="">BUSINESS CARDS</a></li>
        <li><a href="">MAGAZINES</a></li>
        <li><a href="">BOOKS</a></li>
        <li><a href="">WEB DESIGN</a></li>
    </ul>
</li>
<li><a href="gallery.html">GALLERY</a></li>
<li><a href="support.html">SUPPORT</a></li>
<li><a href="contact_us.html">CONTACT US</a></li>
<li><a href="about_us.html">ABOUT US</a></li>
</ul>

nav {
    width: 900px;
    margin: 0 auto;
}

margin-top:0;
margin-right:auto;
margin-bottom:0;
margin-left:auto;