Knoppix 4.0 DVD only boots from VMWARE

Here's the problem...
I downloaded the Knoppix 4.0 DVD ISO and burned it on a DVD using Nero. Then, I tried using it. I inserted the disk into my USB DVD drive and as I restarted my computer, the light that indicates that it is trying to autorun blinked, as it is supposed to. Then instead of going into Knoppix, it just went right into Windows. Oh, this is a HP ZE5185 by the way, and the image was burned correctly. It does boot from CDs, because earlier versions of Knoppix had worked on it. I tried it on the other computer, which also has previously booted from Knoppix, but it also didn't work, and that is a HP 7850. Then I made sure that I hadn't done the dumb mistake of just burning the ISO onto the disk, and I didn't. I started VMWARE and inserted the disk...and magically, it worked...How did it possibly not boot when I restarted? Why DID it boot when I used VMWARE? What do I do?
oh yeah...and tell me if you want more information...
Edit: Due to the lack of help...time to experiment more...oh well...thanks anyway...