Change column width in product detail page

[cglmicro]

I need help finding where to modify the column width of the product detail page.
In fact, I want to :
a) reduce the width of the column showing the image;
b) reduce the width of the column showing the "add to cart" by putting the quantity selector over the "add to cart" button;
c) enlarge the width of the column showing the prices and custom fields so it won't word wrap (see the attach image)

Where to start ?

[attachment cleanup by admin]