How do you create a new initrd image on a linux (2.6) that does not have the mkinitrd script? I've seen that lots of distros come with this script called mkinitrd for creating a new initrd image.

Perhaps there is a generic mkinitrd package to download and install?
If yes, where can I get it?
If no, is it wise to use another mkinitrd script package that belongs to another linux distribution?

Look for a package that contains your distro's mkinitrd command. It is actually a script, and it tends to be customized for each distro.
Creating an initrd file is the last step in building a kernel, so I'm sure your distro should have it.

On my system, the initrd-<version>.gz is a compressed cpio archive. On others it is a compressed ext2 filesystem image. You can extract the files from an initrd image with "cpio -vid < /path/to/initrd". After doing that you can modify the files you want and then use cpio and then gz to recreate it.

It would be better, however, to locate the packages you need. Look for a howto on compiling a kernel. It should say which packages you need, which should include one needed to create an initrd file.

This linux image of mine doesn't seem to have one. I found and downloaded one from a Slackware FTP site and I'm testing it as we speak. Seems to work fine so far, but the real test will be when I boot it. Right now I'm trying to compile some binaries for the initrd.

See ya.

You can actually make one yourself, but it might take a while. The initrd contains a mini-filesystem in a gzipped cpio archive, so you can extract it and look inside with cpio --extract (consult the man page, I'm not sure about exactly how to use cpio).

To make one you do the same thing in reverse. Google "initrd cpio" and you'll find stuff...YMMV