Hi Adeel,
How soon do you need this? I'd need at least a couple of hours and, unfortunately, I am juggling too many things in my life right now. I can only help you in short spurts.
You should also know that writing is not something that comes easy for me. You should see how long I've spent writing my resume and it's still not finished!
I found this link for you on How to Write a Scholarship "letter of motivation" (a LOM is the same thing as a cover letter, right?
) Anyway, read it, apply it to your letter. After you have done so, if you need help with use of English, then I will help you.
http://www.ehow.com/how_2294477_write-scholarship-cover-letter.html
"Dear Madam/Sir, {Try to find out the specific person to whom you can address the letter. If you are unable to, change it to: "Dear Sir or Madam,"}
I have decided to join {The whole point of writing the letter is to get accepted, isn't it? You are applying, not deciding} University of X for MRes
Computational Science. I have done my bachelor's degree in
Computational Physics from University of the X; this degree was started
{I would stay away from the passive voice. You completed this degree, you should be proud of it and write it accordingly!} in 2004 at X and was four years in duration. I have serious intentions
to join X. I think that I have sufficient good reasons to be eligible
for MRes Computational Science. {This sentence is just filling up space; don't clarify, exemplify! Also, stay away from "I think", you have to be more assertive!}"