WRT54GS cannot be configured, need help!!!!

Question

Ok.. I am getting so lost.  I will try to explain the best I can what is going on.  I just bought the Wireless G router with speedbooster and put the CD in to set it up, did everything it told me to do on the screen as far as pluggin cables in yada yada. When it came to step 4 of 4 it said "Waiting for Router". Then after about 2-3 minutes it comes back saying the following:
YOUR ROUTER DOES NOT APPEAR TO BE CONNECTED PROPERLY
Error 322: New router or Gateway not detected
Follow these steps:
1) Make sure you are connecting your new router and not your old router
2) Make sure the ethernet cable from your computer is securely connected to a LAN port on the back of your new router
3) Click retry to try installing your router again
Also, when I try to retry the setup without unplugging anything it says this:
Linksys EasyLink Advisor Setup Wizard has discovered that you are already connected to a router. Many people choose to replace an existing router with their new Linksys Router.
I can connect to the internet without configuring the router!!! It isn't secure though!  I want to configure my router so that it is secure and I don't know what to do to fix this.
I am using a Comcast provided modem, RCA model # DCM425
Any help would be greatly appreciated... Remember I am a noob so please don't confuse me more with words I don't understand.. Thanks
One more thing.  When it is "Waiting for router" the 2 computer icon comes up at bottom of screen saying acquiring IP address so I double clicked on it and it would be connected with the IP address 192.168.1.1 and then all of a sudden it would say Invalid IP address not connected.  I really need help here!!!

Answer 1

Ok, I'm not 100% sure I can help you, but I will try.
First thing, find the setup disk that came with the router and use it as a coaster or a frisbee or something because it is almost completely worthless. 
Until you have completed the setup of the router, I would suggest using a computer that is connected directly to the router via ethernet cable. The reason being, if you change any settings wirelessly, such as security features, you will be disconnected and unable to access it again. So use a computer that is directly connected for setup. 
The IP address you saw in you system tray is the IP address of the router itself. You actually need this for your router setup. Open whichever web browser you use and type in that IP address, nothing else. 192.168.1.1 A login screen should appear for you to enter your user name and password. Leave the user name blank and for the password enter "admin" without the quotes. This should bring you to your basic settings screen for the router. 
From this point, I'm sure exactly how you want to set everything up. If you're not very familiar with networking or routers I would suggest you change very little. If you desire security for your network (which I suggest) click on the "Wireless" tab at the top of the screen. This should bring you to basic wireless settings. From here, you can change the name of your wireless network, change the broadcast frequency and enable/disable wireless broadcast. You can change these if you like or leave them alone whichever you prefer. I do suggest changing the name of you network (SSID) so you can tell which one is yours when you try to connect. It gets confusing when everyone in your neighborhood has a Linksys and all of the names look similar.
Once you're done here, next click on the "Wireless Security" tab within the "Wireless" tap. Make sure you are click "Wireless Security" and not just "Security." From here, you can select the kind of wireless security you want to use. I'm not highly informed on which of these is the best, but WEP is probably the strongest security you're going to need anyway, so I would go with that. After you select WEP you get a few more options. For "default transmit key" just select one. Then in the "WEP Encryption" drop down, select "128 bits 26 hex digits." 64 would most likely be ok, but 128 bit encryption is definitely better. 
In the next box "Passphase" enter a word or short phrase that is only known to you an click generate. The four boxes below will now have you WEP keys. I delete all but the first key to keep things simple, but whatever you want to do is up to you. After you delete the other three lines, select the key in your first line and select/copy it so that you can just paste it into the box in network options when you're connecting to the network. Regardless, I would also write this key down somewhere. If you have multiple computers in the house you have to enter it on each and every one and it's a pain to go back and forth. Click save settings. You're pretty much done. There are other things you can do to beef up security, but this is the most basic and it's still quite strong. 
If you are looking at playing games frequently or anything like that I would go to PortForward.com
Any other questions you have, you should be able to google I think. I hope I can help. Good Luck.