Here's a neat trick: when in doubt and you don't have a grammar reference around, use Google as your ad hoc grammar coach! Just search for each combination IN DOUBLE QUOTES and see which combination returns the most results. The majority of the time, the combination with the most results is the most correct usage. Here are the Google results for all the combinations given by you and One_Eye: "integrate in" - about 513,000 results http://www.google.com/search?hl=en&q=%22integrate+in%22 "integrate to" - about 233,000 results http://www.google.com/search?hl=en&q=%22integrate+to%22 "integrate into" - about 2,110,000 results http://www.google.com/search?hl=en&q=%22integrate+into%22 "integrate with" - about 3,320,000 results http://www.google.com/search?hl=en&q=%22integrate+with%22 (Note: The number of results may change by the time you click on the links above.) Using this technique, you can see that One_Eye's answer is correct: "integrate into" and "integrate with" get significantly more results than "integrate in" and "integrate to".

Well, the Google "ad hoc grammar coach" does not necessarily mean that the right answer is the phrase that returns the biggest number of results, especially in combinations with prepositions. Usually these combinations have slight different meaning or even totally different meaning sometimes. So, "integrate into" (some people use "integrate in") means integrating objects or groups to be a part of a bigger object or a group. "Integrate with" means that 2 groups/objects are integrating with each other, like bringing them together. "Integrate" without preposition generally implies adding new members to a group (usually social). Not sure if "integrate to" is a correct phrase.

Usually you would either use "integrate into" or "integrate with".