Setting up a wireless network in an apartment block

Hi there

I'm a complete newbie at Wireless networks so please be gentle with me!

In short, currently I have a PC, a USB ADSL modem and a fat new 4.6megabit
ADSL connection.

I'm looking to 'sell' my spare capacity to my neighbours who live in my
apartment block. I would like to keep 2megabits for myself and let my
potential customers share the other 2.6mbits.

The block itself is (a) 3 storeys high, (b) timber framed and (c) I live on
the ground floor.

From a technical point of view, I'm not sure if my idea is possible, and
what hardware is required if it is. My questions are..

1) What hardware/software would i need? I'm assuming I need a router of some
sort.
2) Would the signal from the router be strong enough to penetrate 30ft with
2 ceilings in between (if you see what I mean)?
3) How can I make it secure? MAC addresses?
4) How can I throttle the bandwidth I give to them?
5) I don't want to have to leave my PC on all day. Is there a setup that
doesn't need that?

Any help would be appreciated - I'm reasonably technical but not enough
though!

cheers, L