Ok, In laymans terms. Generally, all 4wds have the capability to recieve drive at all 4 wheels. HOWEVER, this depends on what type of terrain you are driving. Lets go back to a 2wd. Put yours in 2wd. Imagine you are now parked on the edge of a road. One rear wheel on the tarmac, the other off in the mud. Now, try to drive off. The wheel in the mud will spin furiously, and the car will not move at all, or maybe just a little. That is because the open differential is proportioning most or all of the drive to the wheel with the least grip.
Now, lets change the diff from open to limited slip. This diff has a set of clutches and springs that automatically reduce the amount of drive going to the spinning wheel, and gives some to the wheel with grip. Hence, the vehicle will move forward to a better degree.
The only way to get both wheels rotating in the same direction at the same speed is to fit some sort of cross axle locking differential, such as Detriot Locker, ARB Air Locker, ect.

So why fit a differential in the first place. Because, when you drive around a corner, the inside wheel travels less distance that the outside wheel. If they were connected solid, the inside wheel would spin faster than required, inducing wear in the tyres, or the outside wheel would spin slower, again wearing tyres. The other BIG thing is the weight of the vehicle, combined with the power and torque induced by the motor, and the torque induced by actually turning the corner would cause a tremendous force to build up within the axle, eventually causing an axle to break.

Now, lets make the vehicle a 4wd. You basically have an exact same axle at the front of the vehicle, as well as the rear. (Lets ignore the steering components for these purposes)
When you move your transfer lever (or push the 4wd button) to 4wd, what you are doing, by a system of gears in the transfer case, is making the front propellor shaft turn at the same speed as the back propellor shaft. This in turn makes the front diff turn, and, of course, the axles. The axles turn the wheels, hence 4wd. But remember back, if with open diffs, as your has, when one wheel on each axle hasnt got traction, then you have no forward motion. Invariably, on a 4wd, it will be when diagonally opposite wheels lose traction, that you will stop. The best way to see this is to find a drain, and slowly drive diagonally over it, so one front and one rear wheel are in the drain. If the drain is deep enough so your suspension hangs, your vehicle will basically stop, with the hanging wheels spinning, and the opposite two stopped.

Free wheeling hubs are just that, hubs fitted to the front axles that allow the road wheels to turn freely, disconnected from the front inner axle and diff. Whats their purpose. When travelling on hard surfaces, in 2wd, by having the hubs unlocked, the front prop shaft/diff/inner axles will not be turning, improving fuel comsumption and lessening front driveline wear.

Getting your diffs done. Your mate means getting your diffs welded, also called Lincoln lockers, or CIG lockers. As no manufacturer makes off the shelf locking differentials for Sportrak/Ferozas/USA Rockys, one way of improving off road capabilites is to have someone weld the side gears to the carriers in your front differential. This will mean that both front wheels will travel at the same speed, regardless of the terrain and traction available. Be aware, that this proceedure is permenant, unless you replace the entire differential, will make your steering very heavy, (lessened with power steering) and could shorten the lifespan of certain front driveline components, notably your inner axles and CV joints. This isnt a problem, however when driving on roads, as you should have your hubs in FREE, which as I said before, disconnects the road wheels from the inner axles.

4wds with things like constant 4wd, traction control, centre diff locks, and various other modern improvements cloud the issue somewhat, and I wont go into them at this point.

Hope this explains things a bit more clearly.
Cheers
David

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