They typical approach is to install a separate instance of SQL Server. But if you know what you are doing, you can select Custom Install and disable SQL Server Express. In that case, you will be responsible for creating the SplendidCRM database and for the credentials to access the database.
As for .NET, it should only install if it does not exist. However, the configuration utility will always run the .NET the ASP.NET IIS utility to ensure that .NET has been registered with IIS.
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