Making Application Database (SyBase, Oracle, MySql) Independent

Hello Experts ,
I am having an application running on SyBase DB and frontend is VB.NET. I would like to make it somehow databaseindependent. Means, I want somthing like on installation time if I specify Oracle then Oracle db to used else Mysql or else SyBase.
Also, is there any solution for the coding too ? means, in case of ORACLE databse the relevent code to be installed on machine, in case of sybase only relevent code to be installed.
I dont want all 3 codes to be installed on machine as it will lead to space problems.
Please send me links , docs at cp.dandriyal@gmail.com
Warm Greeting to all of you.