salam Respected members.
Brother if you have a back ground of physics...I beg you to go for it,because it took me only 6-7 days( I had only 75 days for preps) to go through all the course except for the few probabilistic distributions and Lande G's factor which were intentional delayed.Most of the literature oriented members will always suggest not to opt for technical subjects as I was strictly dis advised by experienced aspirants,but I went a step further to choose Applied Mathematics.But after all, its all up to your taste.Physics will bring extremely solid marks to you if you work on your concepts,However you should follow your own passion.
In my case( March 2010),Both the papers of physics were easy( as usual) which made even my friends motivated for physics.Under extremely worst case scenario,a minimum of 140 marks are expected inshallah.
My preparation for physics included
www.wikipedia.com (main focus,take a topic from syllabus,search on Wikipedia and take notes of every important point).
Search key words of practice problems relative to the topic.you will find lot of solved and useful examples every where.I remember I bookmarked more than 15 websites for physics practice problems.
Fundamentals of Physics Halliday & Resnick ( i went through the book,but will not recommend it for you.
Fsc 1st year and 2nd year book,ensure practice in problem solving.
SSC 9th and 10th physics( I found it very improved)