On your local machine, unzip the file you received from DotNetInvoice. You will see an instruction manual (PDF), and a directory containing the code.
Update the Database connection string in the web.config file using the information provided in the DiscountASP.NET control panel at MS SQL 2005 -> MS SQL 2005 Databases. By default, the database password is the same as your control panel password.
Upload the contents of the code directory into either the root of your DiscountASP.NET site, or into a subdirectory (for example: /billing). If you use a subdirectory, configure it as an applicationdirectory using the DiscountASP.NET control panel: Tools & Utilities -> Web Application Tool.
Delete or rename the index.htm file that resides in the application directory.
Using SQL 2005 Management Console (or SQL Express Management Console), login to your DiscountASP.NET database. Open a new query window and open the install.sql file located in /sql. Follow the instructions in the file to create the database objects.
Test the install: open a web browser and navigate to your DiscountASP.NET website URL found in Account Management -> Account Info/Edit (you may have to use the alternative URL if your DNS has not yet propagated). You should see the client login screen.
Configure your application: Follow the instructions in Section 3 of the DotNetInvoice Installation and Configuration PDF included in your zip file.