Its a difficult subject, you know. If its something you really want to learn, figure 6 months to a year. That will at least get you started. You need to be fairly competant at C before you begin though. If you are not, then double the above estimates.
Here's some tutorials and example programs I've written. The GUI stuff starts at ProgEx37...
That Forger's Tutorial is quite good too. Pretty much a whole generation of Win32 coders started with Charles Petzold's "Programming Windows" books in various editions. They are still available new and used, I believe.