If so then just connect whatever else isn't wireless to the LAN ports on the wireless router. Just buy a bunch of standard straight through patch cables and one crossover cable. You'll not need the crossover at the moment but it's always useful to have lying around.

First step would be to setup the ADSL modem and check that you can access the internet with a computer directly connected to it.

After that you can do the wireless router and the firewall. It shouldn't be that hard to do if you're actually sat down in front of it.