[cflsystems]

You can do this with some css but probably best to modify the options template. The stock options template uses table and for best results of what you want you need to rewrite it to use divs instead. That way you can place them on top of each other, space them out properly, etc just with some simple css. And if anything changes down the road you can still put them back as rows just by changing css.

The template is skin/your_skin/modules/Product_Options/customer_options.tpl if I am not mistaking.