Depends, but in general if ANYONE buys a significant number of shares then chances are the price will go up because of supply and demand. Definitely would need to know more about the specific situation though because chances are the market will react to this quickly and by the time you know, there might not be much opportunity for yourself left.
If the CEO is buying shares on the open market it is a sign that he is willing to put his money where his mouth is. I am always more comfortable buying a stock knowing that the CEO owns shares that he bought on the market, as opposed to those from options or warrants.
When I worked on the Street, that was always a big sucker play. A company or it's executives announce a big share buyback program. They rarely ever complete even a fraction of the purchases, but in the meantime, they get you to buy.
The only insider transaction that has shown any ability to predict future stock prices is when an insider sells stock when it is at or near its lows. Obviously this is a very bad sign. All other insider transactions mean next to nothing.