How do I discover which process is making my hard drive go crazy? (need disk io equivalent of task manager's cpu % column)

Filemon or procmon from the sysinternals suite; process explorer also helps. Free download, unzip and run them as admin user...

If you start task manager and go to the process tab, you can then add columns from the View menu. IO Writes and Reads might show you right away. If not I would go with the sysinternals stuff Bart mentioned.

You might compare snapshots using wmic:

wmic.exe process list io /every:10 /repeat:6

This command will take a snapshot of your process IO 6 times at 10 second intervals.

This command:

wmic process list  statistics /format:list

will give you non-process specific IO as well, like paging file statistics.

Rob