It's very easy to get a six-pac if you're skinny. The biggest problem with seeing a six-pack is mostly that there's a layer of fat above the lower abs so you don't see it too well. But skinny persons don't have that problem (well, most of em -_- )
I would advise you to just work out your whole body, your abs will start showing even if you don't do ab exercises. Or like once a week, only one exercise. I've never done more than that, and my abs are possibly the 'most developed' muscles. Personally I don't believe that you have to train them almost daily. And you'll use them enough as stabilizer muscles while training other muscles.
Keep in mind that if you only train your abs, they'll grow much, much slower than when you train your whole body.
If you do some basic exercises - sit-ups, push-ups, pull-ups, dips, and perhaps some squats (you don't need weights for any of these exercises and you train your whole upper body), you'll see results after about a month or two of training
