User mode network
This is the default networking option for qemu. This does not require root previleges. If you have DHCP running it will take the ip as 10.0.2.15
You can setup an ip 10.0.2.* Gateway is 10.0.2.2 Name server is 10.0.2.3 Netmask is 255.255.255.0
You can setup the pfinet translator with the command
$ settrans -fgap /servers/socket/2 /hurd/pfinet -i eth0 -a 10.0.2.15 -g 10.0.2.2 -m 255.255.255.0
Configure nameserver in /etc/resolve.conf
Setup a proxy with the command
$ export http_proxy="http://<proxy.com>:<port>"
Note: you can add this to your /etc/profile file so that every time you don't have to setup this.
If you are using a direct connection to internet install a proxy server on the host os and use this. (I was not able to use it without proxy)
You might be able to do it using iptables, some clues http://sujith-h.livejournal.com/9520.html
Use scp,ftp... to transfer files, read about sharing files.