This post is intended for non-Muslims, to clear some general misconceptions about Islam.
Allah is God of Muslims only
The general perception among non-muslim is, Allah is God for muslims only, and non-muslims are forbidden to refer God as Allah. For us muslims, Allah is God of everything. Basically, we believe that Allah is your God also, not just our God.
The name Allah means God, as a single entity, where no other power could even remotely rival or challenge Him. It has been used even before Islam, which proves that Allah is not God for muslims only.
So, if you're referring to God as a single entity (Tuhan yang Maha Esa), in which no other power could rival Him, then it is correct to refer Him as Allah, even if you're not a muslim.
Quran is a Holy Book of Islam, and non-muslims may not use it
This is another misconception. Firstly, Quran is essentially not a book. Initially, it was passed around verbally, and it was only compiled into a book after the death of Prophet Muhammad, during the time of the caliphs. Think of Quran as a guidance or a reference, the book is just its physical form.
Secondly, similar to the notion that Allah is God of everything, Quran is for everyone. It's true that Torah (Taurat) is for Jews only, and that Bible is for Christians only, but Quran is for everyone.
You can use it as a source of knowledge, either scientifically or spiritually. In fact, the Big Bang Theory, which was scientifically proven relatively recently, was actually revealed in the Quran more than 1,400 years ago, in a time when no technology exists to prove it. There are many other scientifically proven theories that was actually revealed in Quran hundreds of years before. It would only mean that everything foretold in the Quran is true, and will be proven to be true, in due time.
You can also use it as historical reference. There are a lot of things that can be learned from Quran. We muslims even use it for medical purposes.
By the way, the notion that Muhammad is the author of Quran is another misconception. Quran is the word of Allah, Muhammad is just a vessel in which it was passed to us human. It is impossible for human (or any other being for that matter) to produce such a miracle as Quran. Muhammad himself was illiterate.