Hi,
if you use the link you've postet, you have an actuall version.
Please have a look (as mentioned by aldus) at the file save.php in the folder /install
somewhere about line 228 you should read this:
if(preg_match('/[^a-z0-9_-]+/i', $_POST['database_name'])) {
Please compare it sign by sign.It should be exactly the same.
If it's so, you may have another problem, not the "-"
Regards Bernd