GeeXboX 0.90-4 and above come with a network support for most of the ethernet cards (not all of them unfortunately) and a Samba (Windows shares) support. GeeXboX is running a DHCP client which is trying to autoconfigure your network adapter. Whether you do not get a DHCP server on your network, you'll have to modify the /etc/network file which contains the following lines :
* HOST="" # GeeXboX IP ("" for DHCP)
* SMB_USER="SHARE" # User Login ("" for none)
* SMB_PWD="" # User Password ("" for none)
You can easily modify the IP and Samba Login and Password. On boot, the GeeXboX is checking for remote computers from a common domain and try to automount the Samba Windows shares. Be sure that all of your computers are on the same domain in order to mount all the shares.