I promised another book recommendation and then failed to deliver, so I owe the remarkable Andrew Whitechapel an apology.
My latest passion is for rabbiting about developing for Office in managed code. If your perception of Office dev is solely confined to the world of VBA macros be prepared to be very surprised - the story changes ever so slightly.. okay... hugely with Visual Studio Tools for Office (VSTO to its pals) and even hugelier (?) for the version that'll arrive very soon with Whidbey. Even the story for managed code with the less-than-current versions of Office is much richer than you might expect.
The Office products are of course COM servers, and there's a plethora of techniques that Andrew's book describes for integrating managed code, crossing the managed/unmanaged boundary safely and easily. By sharp contrast with many developer books, it's extremely well written and has a fantastically even pace - never trivialising and never bewildering. The examples (available online) are plentiful, rich, and well documented, so all in all the best £23 I've spent in a while. No, I'm not on commission, and no, we're not related - I just felt that everyone should know about a very sound dev text book!
The book's called .NET Development for Microsoft Office by Andrew Whitechapel, published by MS Press, ISBN 0735621322.