2 errors: SPWIZENG.DLL + autorun.dll: both cant be found

All these started a week ago when I bought a new Vista DVD to install it on one of my desktop. Whenever I use to start the installation I get the following error messages:
“Setup.exe - unable to locate component.
This application has failed to start because SPWIZENG.DLL was not found. Re-installing the application may fix this problem.
The file 'autorun.dll' could not be loaded or is corrupt. Setup cannot continue. Error code is [0x7E]”

I tried running the setup more than 10 times but the same error every time. One of my friend suggested that vista requires cheap RAM memory. I was having 2GB RAM earlier, so I removed 1 stick of 1GB and started installation with 1GB of RAM. Surprisingly the setup completed. I was happy with the same but after the first restart, I started getting the following error messages:

“SPWIZENG.DLL was not found
The file 'autorun.dll' could not be loaded”

I doubt if the Vista DVD itself has the problem. What you guys think? Should I replace the DVD? Or is there any workaround for getting rid of this error? Please help.

No I don’t think this is because the faulty disc. There should be some another reason for this error. You can find the cause of this error messages under \panther\setupact.log file. Did you checked it? If not, check it and reply what is listed over there.

I have been similar situation earlier when installing Vista. In my case I was having two DVD drivers. I downloaded ISO file of Vista and burned it to DVD. I tried installing with both of my DVD drives one by one and got exactly the same error as you getting. After lots of research and troubleshooting I finally updated drivers of my DVD drives and on next attempt the installation went fine. There was no more problem and still it is working fine. So, see if it is not the same in your case.