By and large I agree with seely, but I wouldn't shy away from lower end bikes with Hi-ten, 10-20 or 20-30 or other 'gaspipe' frames. I would not fear the french, either. Nothing will teach you the idiosynchrocies of bike wrenching faster than working on an old French bike. And a nice Raleigh Grand Prix or Atala would be a good starter bike as well.
If you must have a Japanese bike, look for Lotus, Panasonic, Shogun, Univega, or Centurion for starters. If you're lucky you might find a Fuji, Bridgestone or Miyata. All these companies made a full range, from very modest 'bike boom' models to top-of-the-line bikes as good as any mass-production bike made anywhere.
lawked gives good adivce about keeping your eyes open for cheap bikes. This year I've aquired a Gazelle-built Raleigh Grand Prix, Peugeot U08, Schwinn World, Motobecane, and a Ficelle from the dump, all more or less ridable, and a Shogun and an Atala for under $5 at yardsales. And that's just the road bikes!
When you do get a bike, come back here and the Classic and Vintage forum for answers. Do yourself a favor and search before you ask. You'll also find
http://www.bikewebsite.com/ and
http://www.parktool.com/repair/ useful.
Good luck, and enjoy!
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