Wireless Connection to D-link Router


How do I connect an iBook G4 (OS X.3.4) Airport Extreme card installed) to a D-Link wireless router connected to a Verizon DSL modem?
AND/OR, could I use an Airport Extreme Base Station without a modem in place of the D-Link router?
We connect to Verizon's basic DSL with a Westell Wirespeed Model C90 modem. The D-Link DI-614+ Wireless Broadband Router is connected to the modem via Linksys Cable/DSL 4-Port Router (NR041). A PC and an iMac are connected directly through the Linksys router. My son (away at college) was able to connect a PC (but not an old iBook this summer) wirelessly last summer using the D-Link router.
I can connect to the Internet when the network cable is plugged in but have been unable to connect the Internet through the D-Link, despite trying numerous ways. (I was able to "connect"--or so I was told--through a new 802.1X configuration but could not get to the Internet--"...can't find the server".)
I've tried entering the IP address in the router setup instructions and the Verizon IP address. I've tried different passwords(always required when I used the assistant), including a blank, but I always get a message like "There was an error joining the AirPort network 'xxxx'."
The iBook is about 6 feet away from the router, so distance is not the problem.
1. Should getting the Airport Extreme Base Station help (and would I need one with a modem--I can get one much cheaper without)?
2. Any ideas as to why I can't connect to the Internet through the D-Link router?
Thanks in advance.
Configuration based on original post:
'(phone line) -- C90 modem -- (ethernet cable) -- NR041 -- (ethernet cable) -- DI-614+', why?

Try this ...

(phone line) -- C90 modem -- (ethernet cable) -- DI-614+.

..., then - read the DI-614+ product manual, and configure the DI-614+ accordingly.
Thanks. I tried your suggestion, but it didn't work. I still can get a "connected" status but no Internet connection.
Unfortunately, I also called Verizon, where I was referred to D-Link (after lack of success), where I was given advice (that didn't work), then D-Link again, then Verizon again (when the D-Link suggestions left me in even worse shape--the wired computers no longer could connect). However, the Verizon person didn't even know that iBooks were made by Apple, and I don't think he understood the situation. He changed my Verizon password, which never seemed to be the problem (except when I tried to connect my iMac running OS 9.1 using the Verizon software).
My son, who last summer was able to connect his PC (but not an old iBook) to our DSL service through the wireless router arrived home last night, and he was able to restore the connections I couldn't, but he also was unable to get the iBook connected (except when wired).
I've come to the conclusion that I need to just hire someone with a lot of networking experience to come to the house and set up the connection, so I've asked someone from Washington Apple Pi to come over as a consultant or to recommend someone who can.
Thanks for the try anyway.
Oh, by the way, thanks too for the link to the DI-614+ product manual. At least I'll have that for the next guy.
This may not be a solution, although this has worked for other people. Third party router (other than airport), most of the connection problems happen with the level of encryption for the password. In other words, set the level of encryption to the lowest setting on the router. This has been a solution on other situations.
Search the forum, with linksys as your field.
Thanks. One of the tech assistance guys suggested something similar. In the end, after many hours and some expert help, we found a very simple solution--I needed an Airport Express software update! I had updated 12 or so files, including the OS, but it was late at night, so I never checked back to see if I needed another round of updates, after the OS update.
Now, I have an antenna/reception problem--see separate listing.