How/where can I add height to this box? Also, I put three of these boxes horizontally next to each other, but they have no space between them. How do I add spaces between the boxes? Thanks.

CSS code:

/* set the image to use and establish the lower-right position */
    .cssbox, .cssbox_body, .cssbox_head, .cssbox_head h2{
      background: transparent url(img.php.png) no-repeat bottom right}
    .cssbox{
    /* intended total box width - padding-right(next) */
      width:335px !important; /* IE Win = width - padding */
      width: 320px; 
      float:left;
    /* the gap on the right edge of the image (not content padding) */
      padding-right:15px; /* use to position the box */
      margin:20px auto}
 
    /* set the top-right image */
    .cssbox_head{background-position:top right;
    /* pull the right image over on top of border */
      margin-right:-15px; 
    /* right-image-gap + right-inside padding */
      padding-right:40px}
 
    /* set the top-left image */
    .cssbox_head h2{
      background-position:top left;
      margin:0; /* reset main site styles*/ 
      border:0; /* ditto */
    /* padding-left = image gap + interior padding ... no padding-right */
      padding:25px 0 15px 40px; 
      height:auto !important;
      height:1%} /* IE Holly Hack */
 
    /* set the lower-left corner image */
    .cssbox_body{
      background-position:bottom left;
      margin-right:25px; /* interior-padding right */ 
      padding:15px 0 15px 40px} /* mirror .cssbox_head right/left */

Box code:

<div class="cssbox">
<div class="cssbox_head">
<h2>This is a header</h2>
</div>
<div class="cssbox_body">
<p>This is for your content.</p>
</div>
</div>
 
<div class="cssbox">
<div class="cssbox_head">
<h2>This is a header</h2>
</div>
<div class="cssbox_body">
<p>This is for your content.</p>
</div>
</div>
 
 
<div class="cssbox">
<div class="cssbox_head">
<h2>This is a header</h2>
</div>
<div class="cssbox_body">
<p>This is for your content.</p>
</div>
</div>

How do I add spaces between the boxes?

Margins or padding work.

How/where can I add height to this box?

Looks to me like you'd put the height on cssbox_body.

Change your css to something like

/* set the image to use and establish the lower-right position */
    .cssbox, .cssbox_body, .cssbox_head, .cssbox_head h2{
      background: transparent url(img.php.png) no-repeat bottom right}
    .cssbox{
    /* intended total box width - padding-right(next) */
      width:335px !important; /* IE Win = width - padding */
      width: 320px; 
      float:left;
/*////////////////////////////////////////*/
/*Start of height*/
      
    height:400px;

/*End of height*/
/*////////////////////////////////////////*/
    /* the gap on the right edge of the image (not content padding) */
      padding-right:15px; /* use to position the box */
      margin:20px auto}
 
    /* set the top-right image */
    .cssbox_head{background-position:top right;
    /* pull the right image over on top of border */
      margin-right:-15px; 
    /* right-image-gap + right-inside padding */
      padding-right:40px}
 
    /* set the top-left image */
    .cssbox_head h2{
      background-position:top left;
      margin:0; /* reset main site styles*/ 
      border:0; /* ditto */
    /* padding-left = image gap + interior padding ... no padding-right */
      padding:25px 0 15px 40px; 
      height:auto !important;
      height:1%} /* IE Holly Hack */
 
    /* set the lower-left corner image */
    .cssbox_body{
      background-position:bottom left;
      margin-right:25px; /* interior-padding right */ 
      padding:15px 0 15px 40px} /* mirror .cssbox_head right/left */

It will automatically re-set the height for you if you leave it the way you had it before. Your boxes are already spaced fined. I'm not sure what you're talking about with that.

Thanks for your replies. I did add a "height" line, similar to your suggestion, and when i did your suggestion, I got the same result. Please see attached image.

Also, you'll see that the boxes need to be spaced apart. Help with that, as well as, the height issue will be appreciated.
Thanks.