Took a look at your posts again, first you want 3 extra boxes, then 2 on each row and now 1 full width block (video and text besides it)? Are you sure this time?
I recommend to use 2 boxes for that: 1 for the video and 1 for the text.
You need to duplicate the code in file index and file admin > options > homepage. Don’t forget to rename the 2 boxes (for example homecontent4, homecontent5).
In file index, rename box 4: <div class="oneHalf homecontent">
and box 5: <div class="oneHalf last homecontent">
I guess this time you don’t want to have site title, read more and image? You should remove that from the code.
The Custom CSS stays the same:
.oneHalf { float:left; overflow:hidden; width:450px; margin-right:20px; }
.oneHalf.last { margin-right:0; }
.oneHalf h3 { padding:10px 0; }