NATS allows you to display radio buttons as an alternative to a select box on the join option section of the Join Form. To add this feature, go to Sites Admin, then click the Edit Site Templates icon.
Once you are in Edit Site Templates, select the template named join to edit your Join Form. When you have opened the join site template, replace your old code with the new code, below, in the template:
Old: Select Box
<select name="signup[optionid]" class="join_select">
{html_options options=$join_options selected=$vars.optionid}
</select>
New: Radio Buttons
For NATS 4 use:
{html_radios name="signup[optionid]" options=$join_options selected=$join_optionids.0 separator="<br>"}
The $join_optionids.0 variable will automatically set the selected radio button to the first option listed.
For NATS 3 use:
{html_radios name="signup[optionid]" options=$join_options selected=$vars.optionid separator="<br>"}