The visitorID should be stored in the orders table, which then can be linked to the orderdetails table which can be linked to the items table, which is where you are likely storing the download locations.
You could probably use one page and just vary your SQL based on the login, but if you wanted to go to three pages, then :
1) Have the successful login send you to userdownloads1 and store the user_level as a session variable
2) Create a rule called "In group number 1" that checks to make sure a user is in group 1.
3) on userdownloads1 apply the server behavior to redirect to userdownloads2 if they are not part of the group "In group number 1"
4) repeat steps 2 and 3 for each group you want a separate redirect for.