You'll need to use Javascript. http://ryanfait.com/articles/2007/01/05/custom-checkboxes-and-radio-buttons/
what do you mean if you're talking about customizing them with a different image then you will use CSS. but if you're talking about checking one box you use checked="checked".
All I want to do is put a 1px solid border around it instead of that big ugly beveled one. How could I do that using CSS?