Problem of dll versions

My project is in VC++ 5.0. I m using some MFC dlls with version 4.21.7022. If i try to install my application on client’s m/c which is having newer version i.e. 6.00.8168.0 of those dlls, problem occurs. My application files are getting copied but not the dlls and my application do not work with new version of dlls. What can be done in this case?