You can use vde to configure qemu to access the local network:
(from http://blog.bravecobra.com/index.php/linux?p=41&more=1&page=2)

vde_switch -tap tun -daemon
ifconfig tun 192.168.193.225 (some free subnet & address)
chmod 666 /tmp/vde.ctl

Now check with ifconfig whether you see the tun device with the specified 
IP address. That address will act as the gateway for our guest. 

Next we want this gateway to forward packets to the eth0 (our local 
network connection and/or internet connection). To do this we use iptables:

echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

vdeqemu -hda hd.img -boot c

In qemu configure networking to use another IP in the local subnet with a
gateway corresponding the the tun device IP:

    * IP: 192.168.193.226 (some free address in our new subnet)
    * subnetmask: 255.255.255.0
    * gateway:192.168.193.225 (our host tun device)
    * DNS: set it the same as your host OS