Well I have a laptop so it is convenient to not bring the CD drive everywhere.

But that is a problem. I have 3 primary partitions and one extended. That site says I can't boot from a logical partition. What should I do? I need my Fedora boot directory and my Xubuntu boot directory. I don't think it can boot from an ntfs windows. Is there no way to boot from a place that isn't the boot directory with grub? Or boot from a logical partition. (I think it is possible, one guy told me about how to boot from a logical partition before. I don't seem to understand it much myself though.

But that way you showed me doesn't work either.

I typed

knoppix screen=1280x800 depth=24 bootfrom=/dev/sda4/knoppix.iso

It still wants to boot from the DVD at /media/hdc. Why?