:wasalamex
All the religions of the Prophets was Islam (submission to Allah.) That's why the different Prophets might have different social laws, but the main message was the same of monotheism - don't worship anyone except God, they told their people to do good and turn away from evil, they warned them of the Day of Judgment when we would all return to Allah and be judged on all that we did - then those who denied the message and became arrogant would be punished for their disbelief and evil, whereas those who believed in the meeting with their Lord and did good will be rewarded for that.
All the Prophets warned of this, there were 124,000 Prophets and around 300 Messengers. A Messenger usually comes with a newer law, whereas a Prophet might only continue with a law revealed to a previous Messenger.
None of the Prophets said that they follow another religion, and the titles given to other religions only came after peoples names, or tribe names. No Prophet ever named their religion after anyone, they all submitted themselves to Allah wholeheartedly and therefore were Muslims (someone who submits to Allah.)
The people who believed, obeyed and followed their Prophet will be rewarded in Paradise by Allah. After Allah's final servant and Messenger Muhammad (peace be upon him) received the message - everyone, from no matter what tribe or race has to accept him in order to be a Muslim and gain the pleasure of Allah and enter His paradise.
Here's some interesting links;
Prophets of Islam
http://islamtoday.com/show_quest_section.cfm?main_cat_id=18&sub_cat_id=94
And Allah knows best.