I have always got a doubt in these type of silly words which resembles one another....hmmm what to do with kind of pairs they seem to b simple but they are very diff..then i found something interesting is to think a while on the words...get the meaning and then proceed
here u go the diff b/w
"into"
This is its own preposition. You can think of it as answering the question "where?" or better "where to" (since it refers to motion in a particular direction - toward the inside of something)

"As soon as it started to rain, Rasheed went into the house."

(This is the original meaning of the word. The slang use others have mentioned --s in "I'm really into rock music"-- was created in the 1960s.)

These are two distinct words, that sometimes just happen to end up used next to each other.

For example, look at this sentence:
"I just stopped in to say hello."
The word "in here in an adverb attached to its own verb, while the word "to" is a separate preposition (in this case meaning "in order to")

One test for this -- you can stop after "in" and the sentence makes sense.

IF U haven't got it right try
http://dictionary.reference.com/
http://www.differencebetween.com/