There are a few things that you need to look at After your third video there is
That is forcing the 4th and 5th video onto a new line. Remove this.
You also need the containing box to be big enough to hold 5 video's in a row therefore in the css you need to chaneg the size of div class .contentbg, .contenttop, .contentbtm and .content as they are all set to a width of 660px.
I would also ask if you need to set the width on all these elements and arte they all needed? rthe less html and css you have the easier it tends to be to debug.