Prod Listing - Grid display by rows not columns?

I have a grid display set up and running fine.
I have also managed to integrate a vertical scrollbar.
You can see an example page here:
http://www.funkimunkibadges.co.uk/valentinesday-c-106.html

What I want is simply to change it to a horizontal scroll instead of vertical!
Sounds simple, but it seems not, I've spent many hours trying to figure it out but just can't.

I think there are 2 issues I need to overcome.
First is I guess I need to swap the rows/columns around, so it's based on rows, not a set 5 columns like I have now.
I want it instead based on a set 3 rows with as much width as it needs to fit how many products there are.

I found this file: ../includes/templates/[mytemplate]/common/tpl_columnar_display.php
It seems to be the one controlling the grid layout, but I don't understand it enough to edit it :frusty:

The second issue is that if I change it to say 7 columns, they all get squished together, I need them to go off the page so a scrollbar appears.
I think that's in the stylesheet.css but no amount of messing with it seems to allow the above to happen.

Thanks for any assistance!!