For those on Windows 7 it is easy to check the checksum from a command prompt.

Press START then enter CMD in the box and press enter.
change to the directory where your ISO was downloaded (e.g. if you put it in C:\TEMP then type "C:" and press enter and then type "CD \TEMP" and press enter)
Then type this: CERTUTIL -HASHFILE C:\TEMP\WizardOfOz-autobuild-v5.05.iso MD5

You'll get a result that shows

CertUtil: -hashfile command completed successfully.
8a4a45aa5e73bc6b6c0060228f88b41c WizardOfOz-autobuild-v5.05.iso

Compare that to the md5 text file available from JJP website and they should match (adding spaces where needed).

I did the above and my install was seamless.

Check for magnetization like stated above... but also you can adjust how long the ECMB lock stays open (default is 250 milliseconds). I had to put mine down to 230.

Regarding demagnetizing... I'm thinking I need to do it as well.

Saw this (but haven't tried it yet): http://www.pinballnews.com/learn/magnetism2/

and recalled Aurich recommending