Deathshead,
when dealing with currents in a circuit you have to use Thevenins theorem when looking at the devices, and not simple add the currents of each of the devices. (the Algebraic sum of the currents at any node is equal to 0). So if you know your total equivalent resistance for the circuit and the input you can calculate the total current using ohms law.
This total current is then shared to go through parallel devices in the circuit, while series devices will get the whole lot.
eg in your circuit since all are 1K and youve calculated total current as 8mA, the two parallel resistors will each get an equal share (4mA) if the third resistance is then in series with these parallel two, the node between the 2 will sum as +4+4-8=0, ie 2x4mA into the node 8mA out and through the third resistor.
Sorry if this isn't too clear, I think I gave too much information (Simply put, your IT is calculated using ohms law with your equivalent RT, if you want to understand why this is the case then look at Thevenins), too late for theory, if you need a better explaination let me know and I'll sort one out for you.