You are almost certainly wasting your time. In many years as a developer, I only resorted to disassembly a couple of times - once to find a fault in a C compiler and once to diagnose a UNIX kernel freeze. Unless your aims are very limited - to solve a specific problem - the effort involved is likely to be prohibitive, probably by several orders of magnitude.
I dunno about Windows, but on *nix systems tracing system calls is quite usefull in diagnosing problems with software that is less than helpful with error messages and for which you have no source. The tools are "strace" on Linux or "truss" on Solaris. If you can find something similiar for Win, that might help depending on what you are trying to do. Many debuggers have a disassembly facility eg "gdb" on Linux, but as I said you would be wasting your time.