Should I avoid talking after saying the birkat hashachar "haMechin Mitzadei Gaver", but before I have crossed the threshold of the entrance to my home? Also, what if I do not intend to leave my home on a given day, do I still say the the bracha in the morning?
So long as one is walking on his way out one may talk as one does so. The very act of walking is a fulfillment of the action on which you have said the bracha.
In regards to when one does not leave their home on a given day, one should nevertheless recite the bracha in the morning. In the Talmud (Brachot 60b) it simply states, "When one starts to go (or walk) one says...". The Rambam very correctly interprets this to mean when one starts to go about one's daily business (as opposed to when one takes the first step upon waking), such as when one leaves one's house.
It follows that normally you would recite this bracha when leaving your home for the first time on that day, assuming this happens in the morning. If however one does not intend to leave one's house that day (such as someone who works from home or someone who is ill) or he intends to leave the house much later during the day, one should recite the bracha in the morning. On such a day, one "goes about one's business" at home.
The bracha is to remind us of Hashem's hashgaha as we go about our business throughout the day and our lives; this applies at home as much as anywhere else.
19th of Adar II, 5771 25 March 2011