It's not worth buying a 10/100 switch now, Gigabit ones are so cheap.
I have one of these, it's been solid as a rock for over 18 months, and uses about 2W of power at worst when all 8 ports are busy:
http://www.amazon.co.uk/TP-Link-TL-SG1008-8-Port-Rackmountable-Gigabit/dp/B001AUL7A6A 10/100 will work fine, I use a little 5-port Netgear for my RPi and 2x Blades rig, which uplinks to the TPLink. Works fine, it even runs off the same PSU I use to run the Blades, the USB hubs, the Pi and the fans off.
You could plug a wireless access point in to the switch, and connect that to the wifi on your WRT54G. But, it'll be crap - Wireless-G is a bit crap. Just run a cable.