The M62 is a fairly good engine, now if I'm right, your's will be a late E38, and I presume an auto. I wouldn't try and get too much extra out of the engine if it is an auto as you'll likely kill off the box, BMW auto boxes in my experience with them tend to be the weak link (in the older ones anyway) There are a lot of companies out there who specialise in BMW work, and I'm sure there is one who will be able to help with the mapping. I was told my ECU was too old to be live mapped, then found a company that sell a chip you can put in place of the standard one that allows live mapping, so keep looking.
PS mods or admin, if it's ok I'd like to post a couple of links to places that sell BMW upgrade parts for OP to have a look at....