1. Sometimes, Adaptec generally 'see' hard drive geometry differently than other controllers. You will have to force the disk geometry to be the same as it was on the DPT controller.
2. If their is no raid then it acts as a standard scsi host adapter.
3. Don't think you need it.
4. If you have a regular userid/password that will get you a shell prompt, you can see if the permissions on any of the files in /etc/rc2.d or /etc/rc.d
allow you to write to them, and if so modify these to replace /etc/shadow with one from another machine where you know the root password.