How do I configure a Linksys WRT54G to work with my existing Speedstream router as a switch and use the same subnet?

Before I start messing with any advanced firmware, I'm hoping that there is a simple solution for what I'd like to do. I recently installed a Linksys WRT54G router in my living room. In my laundry room/computer cabinet, there is already a Speedstream 2604 router hooked up to the cable modem with an address of 192.168.254.254. From that router, it's hooked to a switch that distributes cables all throughout the house via wired connections. One of those connections goes to the WRT54G.

Now, after hooking everything up, it seems to work. I haven't tried the wireless just yet, but I noticed that the IP address of the WRT54G is now 192.168.1.1. I tried setting it to 192.168.254.44 to get it to work with the subnet, but it didn't work, and I had to reset the Linksys to get it to work again.

The reason I'd like to do this is because I can't seem to browse the contents of any computers that are directly connected to the Speedstream. I try to directly input the  IP address (for example, 192.168.254.5), and it doesn't work. I can't use FTP on it either.

What I'd really like to do is to have the Linksys act as basically another client/switch that shares the main connection/firewall of the Speedstream AND also pump out wireless internet as well.

When I try to assign a range of allowable addresses, it only allows me 192.168.1.x addresses, which does me no good as all of my other computers have 192.168.254.1 - 192.168.254.22 IP addresses.

Is there something simple that I'm missing? Thanks!