I'm sorry.
JAR and JAA are now EASA.
Only for Your kind information, JAA is the authority wich issued tha JAR. JAA stays for JOINT AVIATION AUTHORITIES who issued JOINT AVIATION REQUIREMENTS.
Now everything is replaced by EASA.
I think You are looking for differences between FAA and JAA and there are a lot of post here in WANNABE sectiona on this.
Thanks You Sir.