I want to use my portable drive as a startup drive of Leopard operating system

I have got an imac from apple , I had bought it around around 1 year back , the it comes with sufficient amount of storage acapcity , I had to purchase an external hard drive for my official purpose, but I have got a question arised in my mind , I want to ask that is there any way that will help me to create the external drive of mine to work as a start up drive for my leopard operating system , I will repeat my question as is there any chance that I can start up using a firewire drive with Os X 5.8 installed in my system , because I like a few the programs that does not run in snow leopard , if anyone has any sort of idea on this please do come forth and give your word of expertise in it.

You cannot do it if your system was shipped with only Snow Leopard. But if there were some other operating system installed along with then I think you can do it , I know what will be your next question on this that if you reformat drive would it take a partition a partition and could you install Leopard on one and snow leopard on the other? If that would be your question then my answer will be yes you can; but you I do not think that you will able to boot from the Leopard partition. If you desire to be able to boot it from the Snow Leopard partition, it requires to be GUID partition format (and both require to be Mac OS Extended

Well I do not think that you will be able to install install Leopard unless there is a Mac that is not capable of booting from the Leopard install disc. If your present Mac only came with Snow Leopard then I am sorry to tell you that you are running out of luck; as no Mac can boot from a system which has been launched before it had you can say older than it and the system may be missing with the required hard ware drivers as well drivers).

No, I did not mean that you could essentially boot with Leopard - I just intended that you must be able to install it.... that is what came into my mind I read here; though, as per the people who have posted or are going to post their comments on this here, that may not be right or accurate . So, at this stage, I' am uncertain to make another (maybe wrong) idea except for this: if the portable disk has no data on it (in other words, you will lose nothing except your valuable time), pop in the Leopard disk and observe if you can select the external as an install disk.

If your Mac came only with Snow Leopard, then it possibly cannot do that function or boot from Leopard at this occaseion . Possibly not from a 10.5 install disc, and I do not reckon that it will boot not from a full 10.5 installation on any partition of any hard disk , whether it will be internal or external. No Mac is capable of booting from a system older than that operating system which came with it, since the older system do not have the compulsory hardware drivers for the newer Mac.