More AirPort Express problems and questions - sigh

Question

I finally got my MBP to connect to the Internet yesterday, thanks to lots of help from Tesserex. This evening I tried to connect my partner's MacBook to the network and ended up having to reconfigure the AX because nothing worked again. Now the AX LED is flashing yellow again, and yet I am able to connect to the Internet wirelessly - I am typing this on my MBP. I am indeed confused as I thought the LED should be solid green, indicating good connections all around. Any ideas about this?
I also tried to secure my network with WPA, but this caused everything to screw up again, so here I am with no security and on the Web. Pointers for a newbie would be much appreciated.
I still need to get my partner's notebook to connect to the Web too.
My set up is DSL modem > Ethernet cable to Linksys DSL router > Ethernet cable to Apple Express (AX) port > wireless to MPB (in addition, I have two Ethernet cable connections from the Linksys routher to my two desktop PCs.)
Help would, as always, be much appreciated.
Holly
MacBook Pro 17"   Mac OS X (10.4.7)   2.16 GHz Intel Core Duo processor with 1 GB DDR2 SDRAM

Answer 1

Ok, the Linksys is a non-wireless router, so we don't need to set up any of the wireless-type (WEP or WPA) on it, however, you may want to consider using MAC filtering. With MAC filtering, only the computer's MAC that have been entered into the filter can access the router. That would mean any other network device would not be able to use this router to access the Internet until their MAC address gets added to the filter. MAC filtering isn't hack-proof, but it will make it harder for amatuers to access your network. (Note: This will only be effective for computers that you will have connected directly, using an Ethernet cable, to the Linksys, so you don't need to do this for your wireless computers.)
To setup MAC filtering on the Linksys:
- Open a web browser and point to 192.168.1.1
- Enter the Administrator username and password at the prompt. (The default username is blank, and the password is "admin.")
- Click on the "Advanced" tab.
- Click on the "Filters" tab to select it.
- Click on "Edit MAC Filter Setting" button.
- For each MAC you want to access the router, enter it's respective MAC address into the appropriate window in the following format: nn:nn:nn:nn:nn:nn
To setup wireless security on your AirPort Express Base Station (AX):
AirPort tab (optional)
- Create a closed network (checked)
Change Wireless Security
- Wireless Security: WPA Personal
- Network Password: <create a password for your wireless network; this will be the same password that you will enter when you connect to the network>
- Verify Password: <enter the same password you used in the previous step>
Base Station Options - WAN Ethernet Port
- Enable SNMP Access (unchecked)
- Enable Remote Configuration (unchecked)
- Enable Remote Printer Access (unchecked)
Wireless Options
- Transmitter Power: 10% (Note: If you are having any trouble connecting to your wireless network, you should increase this value. The idea is to find the ideal power where only computers in the house can access the wireless network and not your neighbors.)
Access Control tab (optional)
- + <add the computer(s) that will access this wireless network>