Ok, first of all, I would advise against IM-ing it, especially tar heroin. I certainly wouldn't want all the shit that's in tar floating around in my leg or where ever you decide to IM it, you'll run a very high risk of infection.
Snorting it is out of the question really, so you're basically left with smoking it and shooting (IV) it. So first
check out this page it is one of the best I have come across as far as information for IV drug use.
Here is another site that is a little more basic. After you check out the first one, read up on this one for some extra pointers.
Oh, here is the
BL FAQ for injecting written by PhreeX a while back. This is a pretty good guide for step by step instructions for those new to injecting, I highly recommend you check it out as well. Once you've read up on all this you're bound to have some questions, so feel free to post them here and I'll help you out or one of the many other members with IV drug experience can help you too.
With a little patience and proper safety precautions you should have no problems at all. Just remember take the extra few seconds to be safe and clean about IV drug use, it will take you a long way!
Oh, as a side note, if you're really interested in snorting it, search for "tar heroin" in the Other Drugs Archive, there aren't too many posts that come up but one will tell you how to make it "snortable"...basically it involves taking a pill (of your choice), crushing it up, then adding the tar H to it...