Those who label internists as "general physicians" are kinda missing the point. A "general physician" is more of what a family practice physician does as he sees pediatric, adult, and geriatric patients. An internist deals with diseases that are most common to adults and, more often than not, the elderly. Internists tend to deal with patients who have multiple medical problems, which you won't generally find in a pediatrician's office or, quite frankly, even a family practice physician's office. Diseases most often seen by internists include hypertension, obesity, diabetes (mellitus), coronary artery disease, etc.
Internists are found on in-patient services where they're known as "hospitalists," our in out-patient settings in large muti-physician group practices, HMO centers, or in solo private practice. Compensation generally ranges and is probably most dependent on what region on the country the internist is practicing and what kind of patients he's seeing. An internist in a HIP center in the middle of New York City is probably not taking home as much as a guy in solo private practice or even group practice. I believe the average salary for internists, last I've seen, is somwhere around $140,000.