First point of advice would be to read the threads already on this part of the forum titled "Medical Colleges in Pakistan" and "IBCC Equivalence for Pakistani Medical Colleges". After reading those, feel free to post additional questions.
You're still in time for school starting in September of 2007. FYI, AKU, Shifa, and Baqai are all private schools and have their own admission requirements different from the Pakistani Government's system of admission.
Dow is a government school so you would apply using the same common application that you use for all government schools. One common misconception of the government school system is that you 1) apply to a school individually and/or 2) you get to choose which school you go to. First of all, you apply to ALL government schools within a province with one application and you only get to have a preference of which school you would like to attend. They however are the ones who ultimately decide which school you will attend depending on your grades/marks.
At this point the best thing you can do is get an application from AKU and Shifa and Baqai with a list of the required materials each will require. The government school application has not came out yet for the next year so you'll have to wait on that. If you have finished your O/A levels, you can start working on getting your IBCC equivalence certificate from the IBCC office in Pakistan. That is the very first step in applying to Pakistani medical colleges.
Hope this helps, and welcome to Med Studentz. #happy