I have a question regarding the width of each column in the product listing.

I am running version 1.3.9.f and have looked at the includes/MY_TEMPLATE/product_listing.php file but came to a stop when I didn't see what I was expecting.

Where can I modify the width of each column on this page?

My intention is to customize the view of my listings and I have played with a few mods, but nothing I found does the job.

I would like to do something like this:

Code:
Listing for product1:
| image |   custom specs   |   description  |   price   |
Listing for product2:
| image |   custom specs   |   description  |   price   |
Listing for product3:
| image |   custom specs   |   description  |   price   |
ETC, ETC...
It's pretty basic, but I can't seem to find the page which controls the column width

Thanks for any help !