Regarding the "All Users" on top of the drop list, here's how that can be done:
In selectusers.pl simply move this line
<pre> print "<option value=\"All Users\">All Users</option>\n";</pre>

above this one
<pre> print "<option>0-9</option>";</pre>

and it will do what you wanted for the Show/Edit Users part - however the A - B - C etc. would take more changes.
What I would welcome would be the option to list the newest users (e.g. those that joined within the last 1/2/5 days), and to show the user title and groups in the listing.