In pictures: Taking apart Hewlett-Packard's Prolia...
All HP DL380 G5 servers come with a hex key on the back that can be used for certain rack configurations. The DL380 can be placed in a standard rack with no tools.
There are five PCI slots, although one is normally occupied by the SmartArray controller used to drive the disks. The three slots on the left are full length.
There are two Gigabit Ethernet ports on the back. HP provides an upgrade option to use these for iSCSI as well.
In pictures: Taking apart Hewlett-Packard's Proliant DL380 G5 server