The software requirements can easily be met with Ubuntu Server 8.04 LTS
Once established, you do not want to be changing the server every six months, so a LTS distribution makes sense. Also a server does not require graphics support (a pet gripe of mine, servers are ment to serve data, not draw pretty pictures!).
In addition to the required applications, the server can be used to provide infrastrucuture services including DNS and DHCP.