如何使用PHP将此时间转换并还原到UNIX？

I want to save this date format into my DB 20/07/2012 22:10 in a UNIX format. How can I do this, and how can I revert it to a readable format?

I believe you are looking for on of two possible variants.

//save it
$timestamp = strtotime('20/07/2012 22:10');
$timestamp = mktime(22, 10, 0, 20, 7, 2012); //mktime(h,m,s,M,D,Y)

//retrieve it with
while ($rows = /*...*/) { 
    $timestamp = date("D/M/Y g:i",$rows['timestamp']);
}

Try the strtotime() PHP function. It is probably what you are looking for. To get it back to a readable format use the date() function like:

$date = date('Y-M-d', $unixTime);

As David said, you can use strtotime('20/07/2012 22:20') but you'll have to be careful with the locale setting.

If you feel more confortable though, you can try this:

list($d, $m, $y, $h, $i) = sscanf('20/07/2012 22:20', '%d/%d/%d %d:%d');
$unix_timestamp = mktime($h, $i, 0, $m, $d, $y);