Just save it to a convenient location. I'm not sure what the 1 a) business is referring to and apparently there were no instructions to download any files in the previous step. Maybe I'll try to fix that up a bit. Basically you use the dd program to write the partition table to the boot sector.
dd if=mbr-xxxx.bin of=/dev/diskN
where "if" stands for input file and "of" stands for output file.
Just open the terminal, navigate to the directory containing the MBR that you downloaded and execute the above command. Be careful that you replace "diskN" with the proper disk name for the iPod. (You don't want to overwrite the boot sector of your Mac's HD.)
This brings you to step d).