I have two computers that i want to use my speedstream 4100 b DSL modem on, i was wondering what is the cheapest way or anyway to connect both computers to the one modem?

Assuming you're using Windows XP, the cheapest way is to enable Internet Connection Sharing. A google search will bring up all the info you need to know.

The best way would be to buy yourself a small router with a built-in switch.

Router is the way to go. They only run 40 to 60 bucks USA.
If your using ICS then the main computer must always be on. If it reboots you lose the internet on the 2nd computer.

So do i plug the router into my main computers USB port or the ethernet port? and do i need a hub if so whats it called?

[EDIT]
I was thinking about useing the Belkin F5D7230-4 802.11g Wireless DSL/Cable Gateway as my router, and the Belkin 802.11g 54Mbps Wireless PCI Adapter for my other computer. is this a good way to go?

[Another edit]
If this happens:
It reboots you lose the internet on the 2nd computer.
Will i have to start the connection back up again?

Also will i be able to transfer data to and from the two computers?

The Belkin F5d7230 has a built in switch so both computers will plug into the the router/switch port if doing wired. The wireless will also connect directly to the router.
If one computer goes down the other computer will keep the internet connection. No need to reset connection. You will need to put your login info for the dsl in the router duriing setup.
Setup shared folders on both computers to share files back and forth. May need to make changes in firewall to allow this if your using one, which you should be even with a router in place.

Great, i will come back to this forum if i have any more problems thanks.