Problem in stalling portal5.1

I have tried several times to install 5.1 on my machin but it always says cd doesn't found. I am giving proper path doing according to documenation but no use.
I am downloading software from IBM site and it is specifically mention that for installation of 5.1.0.1 I need to have cd5-1 and 5-3 and I downloaded both of them but couldn't able to execute.

This is frustrating.

I have seen my log files and it shows it is going to WAS_update folder but there is no folder called WAS_update in the CD. It is taking wrong path but I don't know why. Also I am thinking what I simply unjar the files instead of going through installation.

(Aug 10, 2006 5:20:47 PM), MultiPlatform.install, com.ibm.wps.install.DirectoryValidator, msg1, DirectoryValidator: starting checking file: C:\CD4-1\win\WAS_update
(Aug 10, 2006 5:20:47 PM), MultiPlatform.install, com.ibm.wps.install.DirectoryValidator, msg1, DirectoryValidator result: false
(Aug 10, 2006 5:20:53 PM), MultiPlatform.install, com.ibm.wps.install.DirectoryValidator, msg1, DirectoryValidator: starting checking file: C:\CD5-1\win\WAS_update
(Aug 10, 2006 5:20:53 PM), MultiPlatform.install, com.ibm.wps.install.DirectoryValidator, msg1, DirectoryValidator result:

I think the problem is I have previous version of WebSphere already installed.