If you want to play real media files in Debian Lenny, you may not be able to play it. If that is the case or you want to install RealPlayer anyways, just follow the simple instructions.
I have recently switched to Debian Lenny (from Ubuntu Jaunty Jackalope) and it is quite stable. However, I wanted to try the latest stable linux kernel (2.6.30 as of now) in this machine and see how it goes. However there are not much problems, I just wanted to install it. I went to Debian Kernel Archive and downloaded the packages but it does not seem to work. So I headed over to the Ubuntu Kernel Archive and the kernel there worked. This is how I did it.