To share an ADSL connection you need to buy a router and hub. The easiest way to share an ADSL connection is by buying a 4-port router (which is an ADSL modem, router, and hub all in one), such as the D-Link DSL504 model (
http://www.dlink.com.au/products/routers/). If you buy one of these, this you won't need to buy a hub. If you already have a hub that you want to use, then you can buy just a standard ADSL router such as the D-Link DSL500, and connect your hub to it. You can buy one of these when you sign up with an ISP. If you can't afford a D-Link router (they're pretty expensive), you can go for another brand such as Billion, they also make ADSL routers, and I've heard that they are as good as D-Link ones, just cheaper (
http://www.warcom.com.au/?page=shop/browse&category_id=3b8089b4de51e129b66ee5d8099d1a3e) (the $230 billion router you see on that page is equivalent to a D-Link DSL504).
I'm don't know how a cable internet connection is shared, but it probably wouldn't be much different to sharing an ADSL connection, it's just that you need to get a cable router not an ADSL router or something (just guessing here
).
In theory, you can share a broadband internet connection (or even dialup) between computers by using just a normal ADSL modem (not a router) by using ICS (Internet Connection Sharing) which is built into Windows 98 and later versions, but I've heard this is quite a troublesome process and the ICS software is buggy so it's not worth the effort of doing it if you can get a router from somewhere.
There's a good site you can go to read some more info on broadband hardware here:
http://www.ozcableguy.com/