Janet, when the Dremel is mounted on the drill press attachment, there is a set distance between the drill bit and that vertical metal mounting pole that the dremel is suspended from...This is known as a drill press capacity...The same is true for a regular drill press...When someone says that they have a 10" drill press, they have 10 inches of clearance between the drill bit and that post in the back (think about it the same as a 16" scroll saw; 16 inches between the blade and the back of the saw)...This means that if you have a project that has blade entry holes located beyond the capacity of your drill press setup, then you need another way to drill them...By hand is certainly an option, but they might not turn out straight.
So, back to the Dremel setup...In order to use the dremel to drill straight holes beyond the capacity of the drill press attachment, you need to somehow extend the capacity of it...As stated, you can use the plunge router attachment...I've also seen another self-made item (which I think is the subject of this thread) that mounts the dremel on an arm that extends out onto a wok table (but can't remember where I saw it).