Nairobi huh? You'll definately want to get down to the Mombasa area for some dives on the coast. Also, be prepared for agressive panhandling... you're likely to find people will, for example, "help you with your bags" despite your protests, and then demand to be paid for it. It may be helpful to learn some conversational Swahili too.
IMHO is shorthand for "In my humble/honest opinion".
A BP/W is a BackPlate/Wing type of BCD, composed of a contoured plate, usually metal, which is fixed to your back with a harness of some sort. Here's a picture:
The bouyancy bladder, or "wing" is sandwiched between the plate and the tank, resulting in something that looks like this:
It's a very rugged, very simple, very versatile system that is favored by technical divers, but which works equally well for recreational diving. It's much more comfortable than it looks... the plate is made so it doesn't rest against your spine. Lots of folks on the board recommend them for new divers, so that you can build skills and muscle memory from the get-go with the same gear you'd be using if you decide later to persue more demanding decompression and overhead environment diving with double tanks, which can easily be used with this system by simply swapping the wing out for a larger one. Lots of folks here have taken that advice and been happy with it, and very few who've tried it say they don't like it.
On the downside, it's not what most divers use, as few are even aware it's an option. That can lead to confusion and misinformation, as seen in the all-too-common case when an LDS tells people that BP/W is only for advanced diving, that it'll push you face down on the surface, or otherwise drown you in ways that a BCD they want to sell you would not. IMHO, that's a load of hogwash.
If you're interested, Deep Sea Supply has a good setup at a reasonable price, or you could get a plate and single tank adapter (STA) from Hammerhead for $100, get an OxyCheq wing from Scubatoys.com for $250 or so, and rig a simple harness with weight belt webbing and $30 or so worth of hardware. It's best to have someone familiar with them help you out if you go that route though. I'm sure there's a diver on the board who lives near you and would be happy to help.