One, do it gradually -- if you're feeling sick, maybe you should be ramping up more slowly. While muscle can grow quickly, tendons and ligaments take much longer to handle the new workload.

Two, form makes all the difference -- running can either feel heavy and difficult, or lightweight and joyous. But unfortunately, it can take a lot of learning and effort to get to the latter -- good relaxed form is not easy to learn, landing the right way on your foot is incredibly important, for some people things like Vibram shoes help, you might have severe muscle tension preventing good form (see a massage therapist, get a Theracane and use it religiously, etc.), you might have horribly tight hamstrings and need specific stretches for those, the list goes on and on. Me personally, I also had to lose a bunch of weight (getting down to my ideal BMI) for running to feel light and easy rather than painful and pounding.

And third, being in the right mood for enjoying running makes a huge difference too. When I'm not in the mood for it, but I run anyways (because I'm feeling guilty about not running, etc.), I generally stay miserable. But sometimes I really am in the mood for it -- I got enough sleep the night before, I ate a couple hours ago so I have energy, but not so long ago I'm hungry, it's not too early in the day (I'm not a morning person), but not too late either that I'm tired -- finding the right time is huge, and makes all the difference.

Honestly, I love running, but it took a lot of time and effort to figure out everything above that made it work for me -- in my case, years. (And pretty much everything about the programmer lifestyle works against you.) But when you manage to make everything align, it feels great, like you're tapping some kind of primal happiness where you're back on the African savannah tracking down antelope... I'm not even joking.