how do you populate a drop down html box within a form, but populate it with values from a php array

for example

<form name="mname" action="index.php" method="post">
<select name='values'>
<option> </option>
<option> </option>
</form>

i can do it by echoing it out, thus not needing the form, but i really need to get at the value i am echoing in the drop down box later, so was hoping someone could show me how it can be done like this, using php