I've tried to install FreeBSD under Qemu several times. But couldn't to configure my network. And recently I've solved this problem. There are several things you should know when installing freebsd under Qemu:
- you should use FTP servers in passive mode (because you are working through firewall)
- you shouldn't use ping to check network :) it doesn't work
- after each restart you have to run configure dhcp interface. Run dhclient ed0 (ed0 - ethernet card name)
Good luck me :)