There is a stylesheet called 960_24_col.css located somewhere in the theme. On line 54, there's an entry that reads:
.grid_1, .grid_2, .grid_3, .grid_4, .grid_5, .grid_6, .grid_7, .grid_8, .grid_9, .grid_10, .grid_11, .grid_12, .grid_13, .grid_14, .grid_15, .grid_16, .grid_17, .grid_18, .grid_19, .grid_20, .grid_21, .grid_22, .grid_23, .grid_24 {
display: inline;
float: left;
margin-left: 5px;
margin-right: 5px;
}I would just change the float to right.