Hi Krishnendu,
This is the same reply from my thread..
Well SCJP 1.4 n 5.0 have lot of differences if u consider the exam objectives, highlighting a few - Generics, serialization, file I/O, autoboxing and unboxing, Regex, enumerations etc which are added for the 5.0 exam and bitwise operators removed from 1.4
Abt the difficulty level, well SCJP 5 is difficult 4 sure when compared to 1.4, but that again depends on you java knowledge. If you're well versed with new capabilities of java 5 after 1.4.2 version, u'll find it slightly easier.
Abt the importance of exams, well take SCJP 5 if projects in your organization have already moved on to Java 1.5, and if you're still gonna work on java 1.4 and below legacy code for sometime, going for the 1.4 exam is better