Use these settings
[photospace horizontal_thumb=true  num_thumb=4]

Add this to style.css in your theme folder. You may need to adjust to suit the size of your gallery (see comments).

[css]

.photospace{
position:relative;
margin-bottom: 80px !important; /* space for row of thumbs */
}

.photospace .slideshow img {
vertical-align:bottom !important;
}

.photospace .slideshow span.image-wrapper {
bottom:0;
}

.photospace ,
.photospace .thumnail_col,
.photospace .gal_content,
.photospace .loader,
.photospace .slideshow a.advance-link{
width:420px; /* width of main image */
}

.photospace .thumbs_wrap2{
height:60px; /* height of thumbnails */
width:100%;
position:absolute;
bottom:-70px;
left:0;
overflow: hidden;
}

.photospace .thumbs_wrap{
float: left;
left: 50%;
position: relative;
}

.photospace .pageLink.next{
margin-right:0;
}

.photospace .thumnail_col {
float: left;
left: -50%;
width:auto !important;
position: relative;
}

.photospace ul.thumbs {
float:left;
}

.photospace a.advance-link {
line-height: 370px; /* height of main image */
}

[/css]