There's a difference between a fetish and hypersexuality--also known as sexual addiction. For every female who exhibits this disorder, there are 20 males who do, so most of this discussion will revolve around men.
A fetish is defined as erotic or sexual significance being projected onto some (ordinarily!) nonsexual inanimate object. Targets of fetishists' desire can include shoes, stockings, jockstraps, underwear and practically anything not typically considered to be sexually arousing in and of itself. Many people can be aroused at the sight of someone wearing these articles of clothing, but the course of any sexual act with that person, such "accessories" are quickly discarded. But for the fetishist to experience sexual arousal and gratification, he needs to have the article of clothing or inanimate object physically present . He depends on the object for tactile and (usually) visual stimulation. Without it, he's often unable to ejaculate or even become erect.
A fetish is similar to, but not the same as sexual addiction, in that it is repetitive, compulsory and at times ritualized. A fetish can take up considerable time-sometimes hours-involving sexual urges, behaviors and fantasies of the particular object. Some people have just one fetish while others have more than one. Many who possess a fetish find it disturbing, time-consuming and intrusive, not wanting this particular desire and interest to be so compelling. But it does differ from sexual addiction in that it can be incorporated into one's sexual life and not interfere. Often it is the more about the shame around the fetish than the fetish itself. Some in the psychotherapeutic community point to strong evidence that fetishism may lie along the spectrum of obsessive-compulsive disorders.
Those who enter therapy for a fetish typically report experiencing jut as much distress as those suffering from sexual addiction. The clinician must assess if the reported distress derives from shame (based on lack of education about their sexually arousing desires) and to what degree it's interfering with their forming attached relationships, or with any "public" area of their lives like employment or studies.
There's some controversy over how valid and reliable the classifications of fetishes really are. There's also controversy around some of the fetishes-particularly transvestic fetishism-being removed from the DSM-IV, since these activities typically involve consenting adults and do not violate any laws.
I personally agree that otherwise we shouldn't pathologize behavior that isn't pathological! Except for ones that harm children and others that which are illegal, all paraphilias should be removed from the DSM-IV. They may not seem normal to many, but that's not to say they aren't healthy and normal for a given individual.
A partialism is a sexual focus on not the entire body, but only a body part (hair or feet) or bodily characteristic or feature (hair, feet, amputation). Thus, "foot fetishist" is really the incorrect term for someone into feet. He should really be called a "foot partialist."
The good news is that fetishes, partialisms, and other paraphilias can often be incorporated into a healthy sex life with a partner! Therapists should know how to help these individuals and advise these couples.