You can turn a PC into a router using Windows 2003 Server NAT and by using two NIC cards...
You can turn a PC into Network Media Streamer and make XP act like server switch
You can pretty much do anything you want if you have the right software and hardware equipment..
NIC 1 - WAN
NIC 2 - LAN - would go into a 5, 8, 16, 24, 32 port switch
You can also make that router into a wireless router
NIC 1 - WAN
NIC 2 - LAN
NIC 3 - WLAN
You can also make it have 4 NIC
NIC 1 - WAN
NIC 2 - LAN
NIC 3 - WLAN
NIC 4 - WLAN
Depends on how many PCI slots you have..