iMac and Linksys Range Expander

I have an iMac G5 running 10.4.11. It is connected to a wireless network (that Comcast set up) thru a Netgear router. I also have a PC laptop running Vista wirelessly connected to the router. I have read that Vista is not compatible to a Linksys Range Extender and have tried everything from the installation CD to connecting it right to the PC to no avail. So, I am trying through the Mac. The Mac is the device that I need the range expanded on anyways. I have read many threads and tried everything that I can think of to make it work on the Mac. I tried plugging the RE into the router directly, and did get blue lights, but when I unplugged it and plugged it in elsewhere, I got a red light again. I plugged it into the Mac and on Network settings manually set Ethernet connection IP to 192.168.1.50, SM 255.255.255.0, Router 192.168.1.240. I was then able to access the RE setup using http://192.168.1.240. In that window, I changed the settings to match my Mac's wireless settings. My wireless settings for the router are IP 192.168.0.11, SM 255.255.255.0, router 192.168.0.1. I also changed the SSID to match my wireless name. When I went to set WEP security it gave me an option for 4 different Keys and a passphrase. I'm not sure what that means. I skipped the passphrase (because it said it only worked with Netgear equipment) and manually entered the same key code (that I use to connect through the usb wireless adapter) in all 4 key slots (because it told me I couldn't leave any blank). It appeared to be trying to automatically saving the settings in that window. I then went to my network utility and it found the RE. I set the WEP there as well. Clearly I didn't do something right because it still isn't working. To add to my confusion is that I do not really know anything about networking and my neighbor has a linksys router that still has factory settings (apparently) and my system keeps locating. Can anyone help me? I have wasted countless hours on this. In fact, my last attempt ended in complete loss of signal the Mac not seeing the USB wireless adapter. Now I got the Mac to see the wireless adapter but only for a few minutes at a time. Should I just return th RE and get a larger antenna?

p.s. I can't use the Apple Air Port because my computer does not have a built-in Air Port card. I am using a Realtec USB adapter.