Hard Drive space
VortexBox is designed to run on a dedicated box. It uses up about 6 GB for itself and a little more than a 1/3 of a GB for each album ripped. So a 500GB hard drive could hold about 1400 CD worth of music.
CPU
Any 500MHz P4 or faster i686 class processor should work well. VortexBox will not load on Via C5 or any other i586 type processor. The new Intel Atom works well.
Memory
256k RAM is required. With 512K you can stream to several machines.
CDROM
You should use a good IDE or SATA CD or DVD burner. Burners have better laser posissioning and you will get better quality rips.
Player
VortexBox runs SqueezeCenter from SlimDevices so and SlimDevices player such as SqueezeBox or SqueezeBoom will work well. You can also use almost any other type of player including ipod touch, xbox 360, iTunes, windows media player, etc.
Router
A router that can handle many small network packets such as a gaming router will work well. If you are using Wi-Fi for your network players this is very important. If you use a cheap or slow router you will get skips in your music.