I'm not sure about stem cells but the symptoms have been managed with deep brain stimulation. Here is a video of a violin player who had this procedure performed successfully.

To have a cure, you must first know the cause...

"The underlying etiology is not clear but many cases seem to be familial.^[17] It has been estimated that approximately one-half of the cases is due to a genetic mutation and the pattern of inheritance is most consistent with autosomal dominant transmission. As of yet, no genes have been identified but genetic linkage has been established with several chromosomal regions.^[18][19] A number of environmental factors, including toxins, are also under active investigation and these may play a role in disease etiology.^[20] In terms of pathophysiology, clinical, physiological and imaging studies point to an involvement of the cerebellum and/or cerebellothalamocortical circuits.^[21] Recent postmortem studies have demonstrated the presence of degenerative changes in the ET brain, with these changes including Purkinje cell axonal swellings and Purkinje cell loss in the majority of cases and brainstem Lewy bodies in the remainder. These studies suggest that the disease is both heterogeneous and degenerative. In other words, ET might be a family of degenerative diseases rather than a single disease.^[22][23]

However, emerging research based on brain autopsies of 50 deceased ET patients (as of December 2009), showed clear degenerative and pathological abnormalities, including "messy" neurofilaments which can impede nerve impulses. Research by Dr. Elan Louis and colleagues revealed that 80% of autopsied brains also exhibited changes within the cerebellum particularly to neurons that produceGABA, a major inhibitory neurotransmitter. Further analysis showed elevated levels of two neurotoxins, lead and harmane, a heterocyclic amine. Heterocyclic amines (HCA) are chemicals found in some foods. Harmane has been detected in coffee and cigarettes (see: http://www.ncbi.nlm.nih.gov/pubmed/21776263), but is especially prevalent in meats that have been barbecued or exposed to high heat.

Another research^[24] indicates there is a strong link between essential tremor in males and the amount of meat consumed, but the exact mechanism is yet unknown.

Changes in the cerebelleum could also be mediated by alcohol consumption. Purkinje cells are especially susceptible to ethanol excitotoxicity.^[25] The impairment could lead to the abnormal cerebellar circuitry seen in essential tremor and suggests that alcohol may also work as an exacerbating agent in the pathology of this disease.

Chronic ethanol consumption results in a loss of Purkinje cell synapses. However, these synapses are regained following a period of recovery that includes gradual weaning off of ethanol. Continued consumption of ethanol inhibits the recovery of synapses.^[26] This impairment of Purkinje synapses is a component of cerebellar degradation that could underlie essential tremor.^[27]

Chronic alcohol abuse has also been linked to other movement disorders such as myoclonus, ataxia, and dyskinesia.^[28]"

^{http://en.wikipedia.org/wiki/Essential_tremor}

Stem cell research for neurodegenerative diseases like essential tremor and Parkinsons is at a very early stage, ie many questions remain to be answered before it could be used as a treatment (and/or 'cure').

As for 'how', the basic stem cell therapy premise is that pluripotent stem cells - which can differentiate into any kind of cell under the right conditions - could be introduced to replace degenerated cells with healthy ones.

Here is one example of stem cell research for a Parkinsons treatment.

Check for Borrelia burgdorferi infection. Antibiotics might work better.