My grandmother has vascular dementia does anybody know what behavioral difference is between this and alzheimers?

Dementia: Alzheimer's and vascular dementia often co-exist, and treatment is very similar for both. Both have cognitive/memory dysfunction, but the progression with vascular dementia is more stair-stepping down than alzheimer's, which is more gradual. Dementia from a single large stroke looks different than from small-vessel disease. Possibly more frequency of depression with vascular dementia.

Can be quite similar: Vascular dementia causes deficits in the areas of the brain affected by stroke. Alzheimers disease causes problems with memory, language, making decisions, planning multistep tasks. And gradual decline in functioning. Behavioral symptoms - hallucinations, delusions, depression, anxiety, agitation, aggression, irritability, disinhibition, apathy, can occur with both illnesses. Some folks have both.

It depends: Behavioral symptoms depend on where the vascular damage happened. However, in later stages the symptoms of vascular dementia and alzheimer's disease are similar.