Are there vitamins that will prevent or cure blood clots in the legs?

No. There are no vitamins or natural therapeutics that will prevent or cure blood clots. Dvt's or blood clots in the leg are a serious condition and could lead to death if improperly treated. The only medications that help are the blood thinners like Coumadin (warfarin) and Lovenox (enoxaparin) (low molecular weight heparin).
Doubtful. Some vitamins do promote bleeding and blood flow- i.e. large dosages of Vitamin C, but sorry, I would doubt that there is any known vitamin that can "cure" blood clots.
No except vitamin K. The only vitamin that helps prevent blood clots is vitamin k which is found in green leafy vegetables.