Fieldsets with tables inside. How to put them on the same line?

It's not tabular data, so why are you using a table?

There are numerous css fieldset examples to use to make nice looking fieldsets using labels and inputs appropriately. (See http://www.pixy.cz/blogg/clanky/css-fieldsetandlabels.html and http://www.sitepoint.com/fancy-form-design-css-4/ for two quick examples)

If you then want to have the two fieldsets arranged horizontally, you can use display: inline-block