fitting patio doors upvc below damp?

[bullwhip]

Hi there hope someone can help.

I'm goin to purchase a set of bi-folding doors for an extension, ideally i want the minimum step from internal finished floor level to external finished floor level.
The manufacturers of the door have said that the step is 150mm in the door unit (seems prety large) and have sent me the following pic to illustrate.
http://screencast.com/t/bGQhGXLbZxp

My questions are: how do i acheive a seemless transition from interior to exterior without damp problems. Can a course of bricks be removed to sit the door unit below DPC? Any other suggestions?

All responses welcome!
Regards

[welsh brickie]

want you need to specify is a low threashold cill you still have a 150mm upvc cill but instead of a standard upvc frame you have an aliminum strip that fixes directly to the cill.