This is advanced technique I would never recommend for development, usually used as a hack. What's the problem? If you asking you should know the concept:
http://en.wikipedia.org/wiki/DLL_injection[
^] — enough said. There is a whole tutorial here at CodeProject:
DLL Injection and function interception tutorial[
^].
Implement is and post another question is you have any problems.
Please be advised that probably no one is interested to write the code for you, but if you do and have problems, you might get some help. I emphasize it because I cannot see any effort from your side; if your really wanted to get results you would have used Google and got a lot of relevant information.
—SA