The Holy Qur'an states that: all believing Jews, Christians, Sabians and Muslims--all who believe in One God, the Last Day and what was revealed to them, shall enter Heaven.
Obviosly, Islaam recognizes all four as separate religious groups with authentic Revelations from One, Same God Almighty. Qur'anic Message is very clear that a person not following Qur'an may still be a believer as long as he/she believes what came to his/her people from God The Merciful.
Qur'an may be critical of the People of the Book (Jews and Christians who are revealed the Same Book--Bible), but does recognize that among them (just like among the Muslims) there are pious (spelling?), faithful servants of God The Merciful.
Now, someone may bring up the issue of military jihad and those Muslims who believe they must fight everyone for the survival of Islaam no matter what. Again, Qur'an is very clear that a believing Muslim if he must fight a military jihad, provided he was attacked first and it is for the freedom of his people and their right on Islaam, he still must be cautious to fight the war against another people because among them could be believers! Something very important some may not remember at times.