I have never heard of MyahOS, and wonder why you, as a (complete?) newbie, would choose such an obscure distro for your first install! kubuntu and ubuntu are currently considered the top distros for ease-of-use & easy install, so you might think about one of those. kubuntu looks nice, and I like it a lot.
I suggest you backup your essential windows data files before you start. Most installations go smoothly, but yes, you can
still click on the wrong option and accidentally reformat your windows partition(s).
Kubuntu can be run (albeit rather s-l-o-w-l-y) from the install CD, without it touching your hard disk at all, good to see if your hardware is supported. Then you can install it with the "Install" Icon on your desktop.
you install, open a terminal window and type the following command:
sudo fdisk -l
(that's a minus "ell" not "one"!)
This will list the partitions on your hard disks.
Make a note of these, but....
/dev/hda1 will probably be your windows NTFS partition
/dev/hda2 will probably be your 70G FAT32 partition
/dev/hdb1 will probably be your 70G FAT32 "backup" partition
/dev/hdb2 will probably be your 200G FAT32 "other backup" partition
When you choose to install, you can (usually) tell the installer to use the free space on /dev/hdb, but you might have to choose "Set partitions manually".
You need two partitions as a minimum for linux:
which is "root" (give it 29GB)
which is swap space (give it just 512M
Some people like /home
to be on a different partition, in which case allow / just 5GB and give the rest to /home, but this is not essential
for your first install.
Make sure only / and swap (and /home, if you have chosen this option) are going to be formatted, format them as "ext3". Swap gets formatted as "swap". Make sure you are not formatting your windows partitions (you did make a note of which these were, didn't you?)
Double-check everything, then let it continue.
(k)ubuntu will automatically set up grub
so you can dual-boot linux or windows. MyahOS will probably set up lilo
the same way, but I don't know. grub & lilo are both bootloaders and achieve the same thing. I started with lilo, but am now happy using grub, it doesn't seem to matter! Yes, you can change your bootloader lilo<->grub later.
I have heard that the "/boot" for Linux must be on the first hard drive. Is that true?
No, but both lilo and grub will take over the MBR, but don't worry, you'll still be able to choose to boot windows.
Besides, if you are using (k)ubuntu, you can always re-boot from the "live" CD, get to a command line in a terminal, and fix up most things that are messed up (except
a reformat of your windows partition!). Very comforting.
So, just get started, take care, and have fun. People here will help you if you tell them what went wrong, or just what it is that you do not understand.