Yes, obvioulsy the world changed alot during Hebrew's "hybernation".
They tried to use old Hebrew words to create the new ones. But there are lots of words from other languages in Hebrew, due to the fact that those arriving in Israel were from all over the world.
Regarding the spelling - Each Hebrew letter used to have it's own sound. Like in Modern Hebrew there are two letters that are prounounced as a T. However originally these had different sounds. I believe certain type of Jews, pronounce one as a Th sound, as this was it's original pronunciation or something.
Also the Hebrew vowels. When they are written there are many symbols that have the same sound. In Ancient Hebrew they all denoted a different sound or length, but in the Modern variety the length distinction dissapeared.