The signal strength was not too bad (52%) but the PS3 got some network errors and the kid loses the game.
My solution was to buy another router TP-Link WR941 and link the Linksys WRT54G using WDS.
The problem was that WRT54G doesn't have support to WDS. To solve this problem go and change the bios of the WRT54G from the LinkSys to
DD-WRT http://www.dd-wrt.com/site/index. Look up for your WRT54G version and follow the instructions.
The WDS setup was easy, just setup the WR941 as usual (basic setup), like next, next and finish. The WR941 was the primary router (gateway to internet), connected to my ADSL and
as a DHCP server for my network, the IP is 192.168.10.1. SSID Springfield2 and WRT54G IP is 192.168.10.2 SSID Springfield1
The two routers need to operate on the same channel and use the same security settings.
To connect the two routers:
Setup WRT54G as a secondary router.
Put the MAC address of the Wireless on the WDS setup
Setup WDS on the TP-Link put the MAC address of the WRT54g here.