In a sense your .NET will perhaps hep with your common programming knowledge and perhaps a Degree of OO. However, .NET is a specific framework based on a certain problem domain, whereas Java contains Frameworks, but is also applied in other problem domains, such as Desktop Apps and such like. From this perspective Java and .NET can be considerably different, particularly as I understand .NET it centers around VB and C# does it not, which are two proprietary languages? This may cause some syntactical and grammatical issues if you try to match them to Java. Java has some unique design concepts and some minor issues which differentiate it more from other languages - to an extent.
I do not wish to dissuade you at all from SCJP, if you can meet the scope and exam objectives covered in SCJP and you feel you are ready, there is no reason why you can't sit SCJP after all, SCJA is not a prerequisite. My particular opinion is since you are coming from .NET there are basic foundational concepts in Java spread out between J2SE and
J2EE covered in the SCJA which are native ideas to Java, and which I see as invaluable for someone approaching Java from scratch or especially from the background of another Language(s). These are not covered in the SCJP curriculum, as it pre supposes a knowledge of this.
I have to admit Im bias towards the SCJA as I am relatively new to Java, and I took the SCJA recently and found it to be of great help in preparing me for the next step. I am sitting my SCJP in March, and I still refer back to my SCJA notes for help on some of the basics, particularly the language features. Before SCJA i spent about a year of getting into Java before taking the SCJA, as I have only web development background and the nearest I got to OO before this was PHP, and not a strong ability in that either (just solving particular problems without a full understanding).
Again the decsion is yours, but don't rush into something without taking in all is needed, and certainly beware any SCJP, prothletysing, trying to convince you that the SCJP is better to begin with. Its certainly more advanced and a stronger certification for employment, but with that comes anassumed knowledge of the basics which are not covered in SCJP. SCJA exam is a great foundation certification, especially for a neophyte like me, its also quite a new exam.
Take a look at Cameron McKenzie's SCJA site:
http://freemockexamssunjava.scja.com/ExamScam/get.jsp and run through the mock exam, if you are comfortable with that, then you are probably better to go for SCJP, but again, remember, its my opinion. I have blogged on this you can see from the blog link below.
Whatever you choose to do, much success to you, and remember you have taken a great step by joining the Ranch, it is one of the best places to be for Java Knowledge whatever your level, and you are bound to get
alot of help and input.
Best of Luck
