How can I change the checkboxes and radio buttons in a SharePoint list form to be horizontal rather than OOTB vertical to save space?
The easiest way to upgrade forms in SharePoint is using InfoPath. Unfortunately this only works with the enterprise version.
If you don't have that, you can use SharePoint designer to customize the forms directly however you are limited in what you can achieve in terms of changing the controls.
I do believe it is possible using SPServices (see http://spservices.codeplex.com/wikipage?title=$().SPServices.SPArrangeChoices&referringTitle=Documentation)