Where do I get the diskinit and image2disk utility from???

It all depends on what's missing. At the very least you'll need console serial access to the box. If you can get to a login prompt at the console, then you can still boot the system into single user mode to change the root password. If you don't even have that, then you'll need to boot the system with a removable CD/DVD or thumb drive as detailed in the setup guide, in which case you won't need a login and password.

 

 

For single user mode, while at the console, at the moment that the loader allows you to choose or customize the boot string, hit the necessary key to stop the automatic selection, choose to edit the boot string, and add the word "single" to the end of that string. Once fully booted you'll have an opportunity to change the root password.