It sounds like the source ISO is corrupt - perhaps Redhat customer support can verify whether that is true or not, or it may be possible for them to ship you a CD.
Regarding your MD5SUM questions however, I recommend running MD5SUM twice, once immediately after you d/l the ISO to your local drive (to verify that the image file was not corrupted during the d/l) and then again after you have burned it to the CD (to verify that the burn process did not corrupt the file).
The syntax of the MD5SUM command is just: md5sum <filename> and the output will be a long string of numbers and letters. Basically, you just want to compare the string value you get with the reference value for the ISO. In other words, suppose your filename is: disk2.iso You would run: md5sum disk2.iso and maybe your output would be: abc123 Now, if the reference value was exactly the same as your value, then you know your ISO image is intact. On the other hand, if the value you got was, say, 44bd8uj9e then that obviously does NOT match the reference value, and therefore, your ISO is corrupt. Don't bother burning it to CD, because it's guaranteed not to work.
Clearly though the main issue at the moment is to obtain a clean ISO for disk 2. Good luck with it -- J.W.