Connecting to home internet via airport - always need to restart the router

Question

I set my home PC as the main station to connect to my ISP. With a wireless router (linksys Wireless-B), I used to share the internet connection to other wireless devices, for instanace, my palm and ibook, my sister's notebook PC and Pocket PC. once, I took my ibook to an internet cafe, which gives free wireless connection facilities. My ibook obviously scanned the wireless network, and was connected (as I noted from the Summary of the "internet Connection". but, when I activate Safar, it said that it could bring me to any website because my computer is not connected to internet. it's very strange, as the Internet Connection said it's connected to the wireless network. The Safari page suggests me to run "network diagnosis". i follow the instruction, and it says I should restart the router and then it would work. I didn't succeed. A while later, it connected. I thought it was okay.
Then, this problem comes up even when I am using my home's internet connection via the airport. I use DHCP to connect to my home internet connection. though the airport summary page said that it's connected to my router (the IP address is my router's address), again, Safari said my computer is not connected to internet, so it didn't work. I followed the instruction of the Network Diagnosis, it again asked me to restart my router device. I also noted from the Airport Section of the Network Perference that, it says the airport has a self-designated IP addres, so it may not connect to the itnernet. later on, I retarted the router and the modem (without turn on my home PC), the ibook connected to the internet.
i checked the router setting of my home PC. I'm sure that it's open to all wireless user. Strange through, after I update the settings (even though i didn't make any changes, perhaps the action of 'save settings', it's kind of equivalent to the action of restarting it), my ibook's connection works. When my retarted my PC and ibook, the connection problem comes up again.
it's very frustrating. Does it mean that I need to restart my router everytime? What about if I want to connect to wireless hotspot outside?
Please please help

Answer 1

Your problem description is complicated, making it hard to figure out what exactly is wrong. Unfortunately, WiFi does this quite often.
To avoid this kind of problem, you should set up different Locations in your Network Preferences for different places that you connect up. That is, make one location for your Internet cafe and another for home. Leave the Automatic location alone.
For locations you know you are going to connect by WiFi, go to Network Port Configurations and drag Airport to the top of the list to give it priority.
If you have a location, where you want an ethernet connection or want to use your internal modem only, then drag those options to the top. Get the idea?
MacOS seems to get confused sometimes when you switch back and forth between different connections all the time. This will not happen if you tell MacOS where you are by explicitly setting a location.
To get out of a situation where MacOS thinks you are connected to non-existent ethernet connection, go into
/Library/Preferences/SystemConfiguration
and delete the NetworkInterfaces.plist file.