1: Motherboard with a P90 or faster CPU

2: 8 or more Mb of RAM (4 works too... but depends on software used, 32 Mb or more is overkill)

3: Storage media (Hard disk or CD rom)

4 Boot media (Hard disk, floppy or CD-ROM)

5 Sound card (check for compatibility with software used ...best are Creative Labs SB 16 or AWE 32 and 64... so far tested with more
  than 20 different software's and all work perfect)

6 Graphic card (mostly needed for "fancy" LCD output ...not needed by the Linux based players though :-)

7 Control device (can be num pad, joystick , infrared and so on)

8 Power supply (AT or ATX ...check your motherboard) or

 CAR POWER SUPPLY (if used in a car or powered by a 12 V battery)  The power supply described on this page is one of the best i found so far... Built it and it works perfectly :-))

9 LCD display , size from 2x16 till 4x40 (check the software which you intend to use if it supports the size and type of connection
  you have chosen)

 Anyway.... large displays may look cool ...but can be expencive and take a lot of CPU time to run. A 4x40 display requires a minimum 200 Mhz CPU.
Don't forget this is a device to play music ,if you want a lot of display output, simply forget the LCD and hook up a VGA monitor:-) A small 2x16 LCD is enough:-)

9 Case to neatly put in all the things mentioned above :-)