in response to your last question, no. you'd have to say :
$string = 'ive';
$string .= ',six';
//or
$string .= ','.'six';
for your first question, you need to use the function explode.
$var = 'two,three,four,five,six';
$a = explode(','$var);
which would do exactly what you are wanting. there could be some whitespace in the aftermath of doing that, but you coul djust call the trim function and get rid of it
example
$total_a = count($a);
for($i=0; $i<$total_a; $i++)
$a[$i] = trim($a[$i]);
Edit:
devinemke, ur too fast for me =\