Dave,
Debian is definitely one of the most complete distributions out there; usually it's the most up-to-date one, technology-wise, and it is definitely the "purest" one, in the sense that it's 100% non-commercial and 100% open-source.
Running in dual-boot is a breeze. You have the option of either using the Windows menu capability in your config.sys and autoexec.bat, or going with LILO (comes with Debian.) LILO is more powerful, but has a higher learning curve. Debian allows you to read and write your Win32 partitions, provided they are mounted as such.
I haven't ever used WINE, so can't help you there. Generally, I work under Win ME when I really need windows, and under Linux otherwise. Sun's free StarOffice software, plus Netscape pretty much satisfy my office/net needs most of the time. For coding, you don't have the nice IDEs under Linux that you'd have under Windows -- but then you won't want to run those under WINE anyway, since they would produce executables that can't run under Linux! Still, I wish Microsoft ported their Developer Studio suite. Oh well...
Anyway, most of your questions (present and future) are answered on the various howto's and faq's you can find under the debian website, in the "documentation" section. It's another thing I like about Debian -- its documentation base is enormous and very thorough.
------------------
I am; therefore I think.