with wireless extending, you will cut your available network speed in half (half of the bandwidth in to the extending base, half out). not sure how that relates to a second repeater.
also wireless G speeds divided by 11 (not to mention if you only start out at half speed), which is all you would have even if you were all attached to the main base is really not that great.
You could try physically moving the repeaters to a different location in your house. so that different computers were closer to different repeaters (and would get a stronger signal).
If you can run a hard wire to each remote express, you will see much better network performance. since you aren't all sharing the bandwidth coming off the main base.
just set them all up with the same SSID and security settings, but different channels, and your devices will automatically change to the stronger signals as you move around the house.
you could look at Ethernet over power line, as a way to get to the remote stations. if running a traditional cable isn't possible.
