Use the implode and explode functions available in PHP. implode takes an array, and will return a string with all the items in a list. Explode takes a list of items in a string, and gives you back an array. You specify the character(s) that are used as the dividers. For example:
$test = Array('one','two','five','seven');
foreach($test as $value) echo $value.'<br />';
$tstring = implode(',' , $test);
echo $tstring.'<br />';
$test2 = explode(',' $tstring);
foreach($test2 as $value) echo $value.'<br />';
The value of $tstring is just a string, and can be inserted into a mysql field of type VARCHAR or TEXT. Convert the array in question to a string for storage, and then recover the original array using explode.