Computer thinks it is connected to the internet when it's not

Question

I posted this in the "Using your PowerBook" category, but I realized it may have to do with internet and networking than anything else. So I thought I'd put it here too.
When logging into my account on my PowerBook, I get the spinning colored wheel and the menu bar takes over a minute to come up. The dock comes up right away, and the status icons (i.e. battery meter, AirPort indicator, Bluetooth, etc...) load at their normal speed. But I get no menu bar, no desktop icons, and no little black triangle under the Finder icon for over a minute. I can click icons on the dock, but nothing will come up until the menu bar has loaded and the colored wheel disappears. After this everything works fine. Applications are plenty fast. I can fast switch between accounts and mine will come back fairly quickly. However, as soon as I actually log out of my account and then log back in, it goes very slowly again. Everyone's account on the computer does the same thing.
I have noticed that the problem only occurs when I am connected to my wireless network at home and the Linux machine which serves as the gateway/router for my network is not connected to the internet. However, this is the case most of the time because I can't get high-speed internet in my area, so I'm stuck with dial-up.
I have a similar problem with iTunes 6.0.4 on my Power Mac G5 Quad running OS X 10.4.6. The G5 is connected to my wireless router with an ethernet cable and whenever the Linux box isn't online and I put a CD into the computer, iTunes spends a minute plus trying the query the online database for the CD info and won't display the CD until the operation times out. However, if I unplug the ethernet cable, the CD comes up instantly. I guess the OS assumes that it is connected to the internet as long as an ethernet cable is plugged in and it has an IP address. The G5 has no login problems though.
This makes me think that the same thing is going on with my PowerBook, because whenever I turn off AirPort, logins become much faster. I don't think the problem has anything to do with my AirPort card however, because logins are just as fast with it on, as long as my Linux machine is connected to the internet. My theory is that something is trying to access the internet at login because it thinks it has a connection, and it is holding everything else up until the operation times out. Does anyone have any clues as to what could be the culprit?
This may sound crazy but I'm pretty sure I first noticed the login problem on my Powerbook after upgrading it to iTunes 6. That might have been a coincidence though because I also upgraded the OS to 10.3.9 right around that time. I can't remember in what order, but the problem with iTunes on my G5 makes me suspicious because I know that problem started with the iTunes upgrade. Strangely, I don't have the iTunes problem on my PowerBook even though I'm running the same version thats on my G5. I guess it's the difference between Panther and Tiger.
I've tried everything from a permissions repair to a clean erase and install in an effort to fix the login problem on my PowerBook. After I restored the the original 10.3 that shipped with it, the problem seemed to vanish, but as soon I a ran Software Update and installed the latest version of everyting, the problem resurfaced. Unfortunately I didn't realize the correlation between the problem and my internet connection at the time, so it may have been just a coincidence.
I've tried bringing the PowerBook in to the Genius Bar at my local Mac store several times and the problem seemed to mysteriously disappear whenever I tried to demonstrate it there. Now I realize that was probably because I was not connected to my home network where the computer thought it was online when it really wasn't. I'm planning to bring them both in again when I get the chance, but "Geniuses" are few and far between at the Genius Bar and you have to get the right person in order to get anywhere. I was hoping someone out there might know how to solve these problems. Can anyone help?

Answer 1

Believe it or not, that article helped me find a temporary solution. After reading it I realized that the problem did have to do with my DNS settings. I had taken the DNS settings that my ISP gives me when I dial up and plugged them into the configuration for my AirPort card. This apparently caused a problem because, although my wireless network is always on, it's not always connected to the internet. So those DNS settings were invalid most of the time.
I found that as long as I leave the area for DNS servers blank, the computer logs in normally. This further confirms my suspicion that something was trying to access the internet at login. I guess as long as I don't specify any DNS servers, the computer realizes it doesn't have an internet connection through my AirPort card.
So I just created two network locations: one for when my network is connected to the internet and one for when it isn't. In the first, I kept my original DNS settings because they work as long as I have an internet connection. In the second I did not specify any DNS servers. This seems to work fine, but I'd still like to know what is trying to access the internet at login. I've disabled the automatic update feature in all my programs that have it, but that doesn't seem to help the slowdown at login. Does anyone know how I could figure out what program is trying to access the internet?