> Can I use default InterBase library to Connect to my FireBird Database?

Yes

> What r the Advantages of Fib Plus Driver over Delphi InterBase Driver?
>

The Interbase (and Interbase Admin) tab in Delphi contains the
components known as IBX. These components are developed and maintained
by Borland for working with Interbase.

They currently work with Firebird and I am not aware of any plan from
either Borland or Firebird to break compatibility with each other, but
I do know that Borland will not go out of their way to make sure
future upgrades will be compatible with Firebird, or support changes
that Firebird may make to the interface to add new features etc, so I
would personally advise against starting new projects with IBX, but I
don't see any urgent need to panic and rewrite everything.

FIB Plus is one of many other options.
http://www.fbtalk.net/viewtopic.php?id=142

Adam