In escence, radio buttons are used in groups that share the same name, e.g.
Cold<input type="radio" name="button">
Hot<input type="radio" name="button">
Free<input type="radio" name="button">
thus, "button" can only be hot OR cold OR free (sorry, im runing out of ideas

).
But if you want to give the option of multiple selection then you should go for checkboxes. And if you want to know which ones were selected, right now i think that loops can do the work, i mean, evaluate through all the variables if an especific one was "sended" by the user (only the selected ones are posted). There should be easier ways to do it but im too lazy to look for more options, now thats up to you,
cheers
hey, check this out is for php cycles to validate those checkboxes, or visit the javascript section for more options..
http://scriptingok.com/forum/viewtopic.php?f=4&t=118