[CalmLogic]

Is my score sufficient to change the stream from Electrical core to Computer Science(more particularly Software..)??

Of course, the general GRE is just one requirement for admission into a computer science program, and a quantitative score of 700 seems lower than most profiles I read in this forum. For example, for a high ranking program like Berkeley, a score of less than 770 can be a hindrance to admission and would warrant retesting.

More importantly, there are computer science course requirements for admission to most M.S. CS programs (in the United States at least), such as algorthims, discrete math, theory of computation, operating systems, computer architecture, etc. Some universities will allow a good performance on the GRE CS to compensate for this, but even when this is the case, it's very hard for a non-CS major to score well on the GRE CS. In fact, even some computer science professors don't score too impressively. For example, if I remember correctly, one professor in computer science at a state school got less than 780 on the GRE CS when he took it just to find out what it was like (without doing a lot of preperation).

I would strongly recommend contacting the CS grad programs you are interested in after visting their websites. If the e-mail responses aren't helpful enough, your best bet may be calling long distance (via Skype or whatever) to get a quality response from someone who knows something. Ideally, you could get in touch with a professor or anyone else who has experience sitting on the CS grad department's admissions committee.

And does top 30 to 50 fetch you good financial aid??

PhD students get priority. M.S. students get the crumbs

If funding is your number one priority, you should be a PhD applicant to a program that will give you an MS if you quit early. At Berkeley, for example, nearly all of their PhD students are funded:

Q: What about financial aid?

A: We provide financial support for all Ph.D. students. If you are accepted, we will contact you about this. For M.S. students, funding depends on the circumstances of the student, and Berkeley will discuss this with you after you have been accepted.

Most Ph.D. students can count on being funded—including tuition and a stipend you can live on—for their entire stay at Berkeley. You will almost certainly not need student loans. However, you may need to serve as a teaching assistant (TA) for undergraduate or graduate courses at Berkeley. The amount of TAing you'll have to do will depend largely on how much grant money your advisor has. (Theory students usually wind up doing more TAing than systems students. So far, my students fall somewhere in between. As of 2005, funding for engineering has gotten tight.)
Post-docs, of course, are paid a salary—one of the reasons we don't have very many of them.

For Prospective Applicants

To put it another way: Even if you are admitted, you are going to be competing with other M.S. students for a limited number of TA and RA positions. Most of these students majored in computer science for 2 years, so they have a leg up on you in getting a TA position in computer science. Your experience, however, in electrical engineering is an important asset and may be helpful for getting an RA position. Therefore, you may want to apply to a program where your previous experience will be a good fit with the kind of research they do a lot of, like maybe robotics.

Also:

Research experience, although not required, can boost your chances of admission considerably. If you have worked on a research project, please tell us about it and ask at least one of your recommenders to comment on it. If your work is part of a joint project, the recommender should indicate your specific contribution to the project. Include abstracts or reprints of any papers you have published in journals or presented at conferences.

Brown CS: Frequently Asked Questions About PhD Admissions

Also see:

Computer Science Admission Requirements of Top USA Schools « Admission Source

Or, you can do what I and most other Americans in the IT industry do -- just build up work experience and forgo the M.S. or wait until you are with a company that will pay your M.S. tuition. There is nothing in a graduate program that one can't learn on one's own, especially now with MIT, Berkeley, and Aduni.org providing online course materials like video lectures.