Not sure what you would like to do with the Quick Launch bar and the Global/Top navigation bar, there are multiple things you can do:
1. Write your own Navigation Provider
2. Just modify the links using the existin provider and navigation control.
3. Create your own custom control to display the navigation.

Now assuming you would like to change the links on the Quick launch bar or top navigation bar, check the followng article:

office.microsoft.com/.../HA101181901033.aspx

you can open the master page in Sharepoint Desiner, there u'll find a control left navigation , u can remove that control and can place your own ASP.NET menu  control.
along with datasoucr so that at the run time u can get all the links