Venture Capital is a form of "risk capital". In other words, capital that is invested in a business, usually a start-up, where there is a substantial element of risk relating to the future creation of profits and cash flows. Risk capital is invested as shares (equity) rather than as a loan and the investor requires a higher "rate of return" to compensate for the risk.
Venture capitalists tend towards greater risk taking with new and hypothetical technologies than private equity firms do. Private equity firms mostly deal in more conservative efforts with existing companies that have already proven themselves.
Private equity firms use their investment capital in leveraged company buy-outs, distressed investments, or as growth capital for existing companies to expand. Private equity firms are more likely to be used to buy up and consolidate existing companies for a quicker return on investment.
As for the level of management oversight, venture capitalists typically are less intrusive in the daily operations of the ventures they fund. Private equity firms generally have a great deal of management control to see the investment grow or to know when a business can be more profitable to them through resale, merging, or liquidation.