In fact, you can easily create a new project which is using the previously set database. At the second step of the project setup wizard (Go to administer your project), you are prompted to chose the type of the database and its version. This is where you can point to the name of the old database. Sitefinity creates its tables over the other files. Every time you access the web site, the application uses the necessary information from the original DB.
For more information, please check the Creating Projects
section from the User Manual.
Hope that the provided information is helpful. Please do not hesitate to contact us if you have any other questions.
the Telerik team