HELP : BPW7 -> Dephi

I have a larg application developed under BPW7. The app include several
windows in inherited chain with TWindow at the base of the chain.
Moving to Delphi, I need to convert to a Delphi base class which will
function like TWindow.
Can anyone, who faced that problem advise me on the easiest way to
convert to delphi classes with as little changes as posible in my old
windows object herarcy?