I use 7 PC´s for the cockpit:
PC1 : FSServer. Asus P5LD2 Motherboard with P4 630 3Ghz @ 3,4Ghz ,2048mb Corsair DDR2 Ram PC 533, MSI 8800 GT 512mb Display card,2x Seagate 200Gb serial ata with raid 0, FDS G1 card for MCP. Software :WinXPSP2, FS2004 with Ultimate Terrain and FSGlobal 2008 Mesh, PM MCP and PMSounds.
PC2 :Captain GC. MSi Motherboard with P4 2,4Ghz,512mb Ram,Geforce FX5400 128mb,40Gb HD. Software : WinXPSP2 ,PM Captain PFD/ND.
PC3 :F/O GC. MSI Motherboard with P4 2,0Ghz,512mb Ram,Geforce 4 FX 64mb,40Gb HD. Software : WinXPSP2, PM F/O PFD/ND. and Simboards Controler Software for Mip and Pedestal
PC4 :Online/EICAS. MSI Motherboard with P4 2,8Ghz,1024mb Ram,Geforce 4 64mb,2x 80Gb HD raid 0. Software :WinXPSP2,PM EICAS,IVAP,Ivae,,SA_WXR weather radar, PM GetWeather.
PC5 : CDU. P3 866Mhz, 256mb Ram, Matrox G450 16mb,20Gb HD. Software : WinXPSP2,PM CDU ,Remote CDU and PMSounds.
PC6 : PMSystems. Industrial 19" PC with P4 2,4 Ghz,512mb Ram,20 Gb HD,Graphics onboard. Software : WinXPSP2, PMSystems and Simboards Controler Software for Overhead, TSR Boeing 737-NG program .
PC7 : FS2Phidgets controler software for throttle
The I/O System will be Simboards from FLIGHTDECK TECHNOLOGY.
Today arrived a lot of Simboard Stuff ... :-)

For the whole Sim I´m gonna use :
2 USB Master Module
2 USB Input MAXI Modules
1 USB Output Module 128 nodes
1 USB Output Module 64 nodes
4 USB Output Modules 16 Digits
White SSD´s with Display-Holders for Radios etc. I will use colour filters to get specific colours.