problems accessing back ups in Time Machine

I have recently wiped my hard drive and reinstalled Mac OSX 10.5. After I did so I have realised it didn't make a difference in performance so now I would like to to back to my configuration before I reinstalled Leopard. I went into my Time Machine and I can see my different backups, however, I can't access them. I can restore to backups made after I reinstalled Leopard but not the ones before the reinstallation.
When I look in my backup folder on my external hard drive I can see every single backup both before and after the reinstallation but I cannot access them.

does anyone know if I can access them and reinstall my OS X to a previous configuration? Should I reinstall the OS X based on a backup? If so, how do I do this?

I am on a macbook pro from 2008.

I really hope someone is able to help out!

Cheers guys!