Hi Tom,
It is possible to use radio buttons. You will need to find the file /includes/functions/custom_computer.php. Around line 80 you should find:
return tep_draw_custom_pull_down_menu($name, $mb_array, '', $parameters, $systype, $fsb, $number);
// return tep_draw_custom_radio_field($name, $mb_array, '', $parameters, $systype, $fsb, $number);
Comment out the first return and uncomment out the second one.
I'm rather confused with your second question b/c the purpose of CCC is to let people configure computers by selecting different components. If you could expound on this question, that would help.