specs help to ensure the releases you are trying to install will work on initial boot. another bit thing that might help (both you and us when helping you) is to use the boot flags "-f -x -v"...
as what they do and why to use them are the same I'll just state them right out.

-f is a "force" flag. it tells the kernel to load using the kernel extensions found in the "/System/Library/Extensions/" folder on whatever drive you are trying to boot from (DVD/HD).

-x is a "safe mode" flag much like windows. it causes only the extensions that need to boot the system up to a bare minimum. (helpful for installs since not much is needed to ensure this works)

-v is a "verbose" flag. This gives a readout of what is going on with your system while it boots. It helps users/debuggers see what their system is hanging on or loading (if you can read the text fast enough). If you are getting kernel panics it will also help point out what is causing this.

More help can be found throughout the forum by simply reading issues (even if they are unrelated to your system) as this will give you more insight to how the OS works.

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