Changing exe starting address to my executables.

Hi
I am sending this problem again .
I want to run my program before any executable.
For that
I am changing following things in the header of first executable.

First.ss = second.ss
First.sp = second.sp
First.ip = second.ip
First.cs = second.cs

First.(number of bytes on last sector ) = (size of (first.exe) + size of (second.exe))%512
First.(total number of sector ) = (size of (first.exe) + size of (second.exe))/512 + 1

And after that adding both exe

First.exe
---------------------
| |
| First.exe |
| |
|--------------------- |
| |
| Second.exe |
| |
| |
----------------------
c:\>first
then firstly my executable should run ( ie second.exe)

It suppose to run but it is not working for me can any body help me out .
OR is their any other method....

after some validation from my program i have to decide whether first.exe will run or not.

If condition is that i have to run first.exe again than how to swap address again. And if not then how to do it

Help me out.

Thank You .