need query help

this is a little over my head but i’m trying to work through it.

if you look at this page you’ll see that’s its pulling in the pictures and titles from the different posts.

i’m using the code here to make it happen: http://pastebin.com/zJmiieDv along with this css:

.project-box-1 {float:left; padding-left:0; width:300px;}
.project-box {float:left; padding-left:29px; width:300px;}

the problem i have is when there’s more than 3 posts, the first one that appears in the second row has the attributes of project box, but i want it to have the attributes of .project-box-1.

how do i alter my code so that the first item and every 3 after that have .project-box-1 assigned to them???

please advise. thanks!