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Java 5.0, a number of new language features were added (for example: generics, auto-boxing, a new syntax for the 'for' loop, etc.). You'll have to learn those new things if you're going to do the SCJP 1.5 exam.
In my opinion it is best to do the newest available exam (1.5), because it will become obsolete less quickly, and so is more valuable, than an older version.