If you're lucky, you already have lots of experience with both Object
Pascal (or, as it used to be called, Borland Pascal With Objects--
essentially, Turbo Pascal v5.5 or later) and with Visual Basic. If you fit
this description, then Delphi will be a breeze for you.
Okay, now for everyone else. In order to make full use of the Delphi
environment, you have to know Pascal, you have to have some grasp of object
orientation, and you have to understand event-driven programming. Once
you're over those three hurdles, you've pretty much got it. See section 5
for more information.
On the other hand, most people don't need to make "full" use of the
environment. If you just want to pull a simple application together that
doesn't do anything too fancy, Delphi shouldn't be any harder to learn than
VB--it's just that there's a whole lot more you *can* do in Delphi, which
will make you feel more lost than you really are.