ok, I just installed Sabayon today, because I read that it had good wireless support. Wireless is the only reason I've been holding on to Windows on my laptop. Anyway, I got the same as you. I configured the connection with WAP key and all, and it just stopped on 28%. To fix this, I had to enable SSID broadcast on my router. I've had it disabled, thinking the less ppl that can see my WLAN the less harm can be done, and it was working fine under windows. So, if you have disabled SSID broadcast, try to enable it.
Finally, I can delete the windows partition on my laptop!! and I'm excited to start using Sabayon full time