How do I use radio buttons properly?

[fashunphotog]

MarcoH64 has been a great help, thank you! :-) Now, I have a question regarding the proper usage of radio buttons and checkboxes on forms.

I've got a form which my customers fill out which they need to be able to edit regularly. If I use a textbox and assign it a value then when they fill it out and return to re-edit the form their previously loaded data is there ready to be either changed or left alone.

To use a radio button it was suggested I use an array - $data[whatevernameIneed]some_value - which works but how do I change the data if I need to? For instance,

<input type="radio" name="tattoos" value="$data[tattoos]yes">

works but I can't clear the data out when I re-edit the form. Is it possible to use an if statement in the array? sort of like $data[tattoos][if 'checked' yes else no]?

Thank you for your help.

M.