Reddit mentions of Felson's Principles of Chest Roentgenology Text with CD-ROM (Goodman, Felson's Principles of Chest Roentgenology)

Pick up a copy of Felson's. It's a classic text for CXRs, and though I'm usually loathe to recommend an entire book for something, this one is a workbook of sorts where there are a lot of pictures and fill-in-the-blank type questions. I think I read the whole thing in 4 hours or so and it's still the basis of my CXR search pattern.

While I think every MD should be adept at looking at a CXR, as a family doc I wouldn't try to read any other kinds of radiographs or cross-sectional studies as final. I'd wait for the rads read on those. Fractures can be subtle. Free air can be easy to miss. Sometimes all you're looking for is a subtle misalignment of, say, the TMT joints, and missing something like a Lisfranc injury will get you sued.

I would relax. Step 1 isn't exactly a pleasant experience. I went on vacation between Step 1 and starting MS3. I'm thankful I did because I had a miserable first half of MS3 (Surgery, Medicine, OB and Peds in the first half of the year). Yuck.

If you just cannot help yourself, and you HAVE to read something, then I would have to err on the side of EKG's. I think you would be better suited to truly understand them so that when you become an intern and your patient on the floor has new onset chest pain, you have a clue.

Radiographs, if you're interested, go for it. If you truly want to go this route: This is the way to go. It is a quick read and will get you through the basics.