There are significant differences in both but both have same fundamentals. Mainly EJB 2 entity beans have been replaced with JPA. There are new features added as well like annotations etc...
...as a EJB beginner do we recommend to start with a Ejb 2.0 guide like Head first
There might be so many projects using EJB 2 currently. But if you start with EJB 3 it won't be difficult to work with EJB 2 either