I was wondering what are the main differences between vascular dementia and alzheimer's disease?

See below: Vascular dementia usually has more sudden onset due to the inadequate blood flow. Below is more detailed description of the disease. http://www.alz.org/dementia/vascular-dementia-symptoms.asp.

Briefly,: Ad progresses slowly, but it does progress. Vd occurs suddenly and stabilizes. With additional incidents, it again abruptly worsens, then stabilizes. Depending on the site of the damage, motor function will or will not be involved. Ad may take a long time to effect motor ability. It's a bit like "disease vs injury". Below is a link since 400 chars is too little. Hope it helps.