I've been given a customer address database.

Now I should write a data source that brings this contatcs from the database
into outlook (like the personal address book).

I never developed an office extension so I absolutely have no idea where to
look first.

Can you please give me a hint at where to look first to make such a addon
for Outlook and what time/effort that would be to implement in average (just
for enabling outlook to pick a adress out of the lot), so that I can get a
rough overview about the task?