You need to configure the prefix manually. The file should be /alp/includes/database_tables.php.
I don't have my computer so I can't tell you exactly which file you need to modify. So you will have to look for yourself.
Also you need to make sure ALP is using your cart's database and not its own. It relies on the configuration key to make sure it is installed against your shopping cart.
I won't be able to respond easily however as Hurricane Ike left us without utilities, power, internet, phone etc as well as a place to live. I don't know when I can post back or when I will have Internet again.
If anyone else can help get this installed I would appreciate it.