Create my own boot.img for rooting? Among the files needed to root an Android device (such as superuser.apk and su), an unsecured boot image is also required (boot.img) to allow for the installation of the superuser and su. 

I understand the theory behind the unsecured boot image (ro.secure=0 set in the ramdisk) - is it possible for me to make this file myself? Or at the least, where can I download it independently of the zip packages that it usually comes with? I'd prefer to create it myself or download the file from the source rather than rely on zipped packages (for version tracking and change logs).

Thanks!
You generally don't need to edit the boot.img to root your phone.
What's your phone model, so we can give you the instructions?

Edit: To root a Galaxy Nexus, first you have to unlock the bootloader, which is really easy since the GNex is a dev phone, just google how to unlock the bootloader, and follow the instructions. I recommend droid-lifes tutorial, but anyone should do. Then all that's left is the rooting.


First you have to download this zip file
Then unzip the file anywhere on you computer, like C:\gnex\
Install the Samsung drivers that are in the zip
After you have installed the drivers, turn the phone of and connect the USB to your computer and phone.
Open a command prompt from the start menu, then move to the directory you unzipped the file to (e.x. cd C:\gnex)
Now you have to boot your phone into fastboot mode, by pressing and holding both the volume-UP and volume-DOWN buttons and then press the power button.
Next, type fastboot devices into the command prompt you opened earlier, and check that your phone is in the list.
Now we have to soft-boot an insecure boot image by typing fastboot boot boot.img into the command prompt
When the phone has rebooted, open settings, and go to Settings -&gt; Applications -&gt; Development and check in the USB debbuging option.
Now execute all of these following commands, after each other, in the command prompt:


adb root
adb remount
adb push su /system/bin
adb push Superuser.apk /system/app
adb shell chmod 06755 /system/bin/su
adb shell chmod 06755 /system/app/Superuser.apk

Now your device should be rooted and ready.