Is it posible to add an ACL Type such as "New" besides the default ones: "Edit", "List", "Import". In my application I need two ROLES, one that can only add new records and the other that can only update records.

I want to do this just for one area, let's say CONTRACTS, could you please post the necesary steps ? Thank you

Then that makes it much easier, but still difficult. 

First, edit the stored procedure spACL_ACTIONS_Initialize and add your new actions.
Second, edit the ~/_code/ACLGrid.cs file to include the new actions.  This may be as simple as adding to the list, or this may require additional logic.
Third, in the ~/Administration/ACLRoles/EditView.ascx.cs file, you will need to get the new action from the grid and update the database.
Forth, in ~/_code/SplendidInit.cs, look for the LoadUserACL and InitModuleACL methods and add the new actions.

It may be helpful to search all the code for ACLACCESS_EDIT and follow duplicate any code around what you find.