OK...
Steb by step:
1. make sure your cables are properly connected: DSL from wall jack into DSL port on your modem/router, and LAN from LAN ports into your LAN port on the iBook.
2. Press and hold reset button for 5 seconds, this will ensure that all settings are at their factory defaults.
3. On your iBook, open System Preferences

, go to Network

, from show drop-down, choose Built-In Ethernet. Make sure your setting are as follows, Configure IPv4: Using DHCP:

If you don't see this option, go to PPPoE tab, and uncheck Connect using PPPoE checkbox, then go back to TCP/IP tab and, make sure you have Using DHCP in IPv4 now.
Click on Renew DHCP Lease.
Make sure in your IP Address it says 192.168.1.2
In Subnet mask: 255.255.255.0
and in Router: 192.168.1.1
IF IT DOESN'T STOP AND POST BACK.
Leave DNS Servers, and search domains blank, and click Apply Now.
Close system preferences.
4. Open up your web browser. Type:
http://192.168.1.1
When you see login screen:

type: admin as username and admin as password.
Verify that DSL status is Disconnected
Lan IP is 192.168.1.1
DHCP Server: Running.
5. Go to Setup Screen:

Click on Wireless settings.
Check enable AP box, and enter name of your wireless network in SSID box. (it can be anything you want, no spaces and better to keep it short..)
Click Apply
NOTE: At this point your router can accept clients oner wireless connection, dsl connection is not active yet, but wireless network is, right now IT IS UNSECURED, so anyone in range can connect.
It is always a good practice to secure it, check in the manual, they explain it there. Any questions, ask.
6. OK, now click on Connection 1 button (big square button, towards the bottom.

Enter your username and password in appropriate boxes. (check with your ISP if you don't know it, usually they give you some sort of a booklet with that info)
Make sure Nat box IS CHECKED, Firewall is optional, i would leave it UNCHECKED, until you verify all is working, then turn it on.
Click on Apply
7. Click on tools tab, then click on system commands, then click on Save All.
Router will restart, Go to Status tab, see if beside WAN it says connected, if it does, GOOD, if it doesn't.... the fun begins here, it can be many different settings, beginning with wrong PPP type (PPPoA instead of PPPoE), or one or more of these extra properties. First change PPPoA to PPPoE in Connection one, basically go through step # 6 again, but use PPPoE instead of PPPoA.
After you change it, do save all again, and check status. If it's connected, good, if it's not, you will have to call your provider and verify the settings for you.
8. If status shows wan as connected, go to Tools tab, and click on ping test button (on the left)
type in this in IP address to ping:
216.109.127.29
click on test.
it should say something like xx bytes from 216.109.127.29, xxxxxxxxxxxx
If it works, check if you can open any websites on your powerbook. If you can't post back.
NOTES:
As you can see there are many things that can be configured in different ways, Apple BS don't have most of these extra settings, so it is easier to make them work, but they are not as flexible, and you would need to use external modem.
DON'T FORGET to enable firewall if all is working well. AND DON'T FORGET to secure your wireless network. (check the manual, or post here)
Good Luck!