debuging

[unix_semaphore () yahoo com br]

hello,
  I am a newbie in win32 software hacking.
  when i have a open source software,i use the gdb to debug the software,but the most of win32 app, is not a open 
source,why i know the functions?the operations?what tools i will use to this?
  For example is simpliest search buffer overflows in open code,why to do this in non open source software?

thank´s