As far as I know, you should be able to start executing code at any memory address in your executable, but you wouldn't know that address anyway.
As for actually running an executable that is WITHIN another executable, I'm pretty sure Windows is not capable of doing that. Therefore, the only way to do that would be to find the adress where the executable started, extract it, write it to another file, and execute. Or, you may be able to find an Windows executable emulator or something like that. It's unlikely though.
What exactly is your aim in all this? Maybe there's another way to go about it.