Ok so we hav guides on Acer, Apple to Dell, now we hav one of my favourite brands: HP

Workstation
HP xw4300 Workstation

OS
Microsoft® Windows® XP Professional SP2
Processor
Intel® Pentium® 4 Processor 521 with HT Technology and EM64T (2.8GHz, 1MB L2 cache, 800MHz FSB),
Or Intel® Pentium® 4 Processor 630 - 670 with HT Technology and EM64T (from 3.0GHz to 3.8GHz, 2MB L2 cache, 800MHz FSB)
Or Intel® Pentium® D Processor 840 with EM64T (3.2GHz, 2 x 1MB L2 cache, 800MHz FSB)
Memory
Maximum 8GB
I/O slots
3 PCI, 1 PCI-Express, 1 PCI-Express x4 (x8 connector), 1 PCI-Express x16 graphics
Drive controllers
Integrated four-channel SATA 3Gb/s controller with RAID (optional Ultra320 SCSI controller/drives or Ultra320 RAID controller)
Storage bays
6 Bays - (3) external 5.25", (1) external 3.5", 2 internal 3.5"
I/O ports
1 x Serial port (2nd optional serial port available), 1 x Parallel port, 3 x Optional IEEE 1394 ports (1 front, 2 rear), 1 x PS/2 keyboard, 1 x PS/2 mouse, 8 x USB 2.0 ports (2 front, 6 rear), 1 x RJ-45 Network, 2 x audio ports (front: headphone and microphone)
Removable storage
48X CD-ROM, 16X DVD-ROM, 48X CD-RW, 48X DVD/CD-RW Combo or 16X LightScribe Dual Layer DVD±RW/±R
Graphics card choices
ATI FireGL V3100 (PCI-Express), ATI FireGL V5100 (PCI-Express), NVIDIA Quadro NVS 280 (PCI), NVIDIA Quadro NVS 285 (PCI-Express), NVIDIA Quadro FX540 (PCI-Express), NVIDIA Quadro FX1400 (PCI-Express), NVIDIA Quadro FX3450 (PCI-Express) or NVIDIA Quadro FX4500 (PCI-Express)
HP xw6200 workstation

Operating system
Microsoft® Windows® XP Professional
Processor
(1) or (2) Intel® Xeon™ Processor 2.8GHz, 3.0GHz, 3.2GHz, 3.4GHz, 3.6GHz or 3.8GHz
Memory
8GB (For greater than 4GB memory support, a 64-bit operating system is required)
I/O slots
4 PCI, 1 PCI Express x4 (x8 connector), 1 PCI-Express x16 graphics
Drive controllers
Integrated dual channel SATA/150 controller with RAID (0 or 1) capability
Storage bays
4 Bays - (2) external 5.25", 2 internal 3.5"
I/O ports
1 x Serial port, 1 x Parallel port, 1 x Optional IEEE 1394 port, 8 x USB ports (2 front, 6 rear)
Removable storage
48X CD-ROM, 16X DVD-ROM, 48X CD-RW, 48X DVD/CD-RW Combo or 16X LightScribe Dual Layer DVD±RW/±R
Supported leadership graphics card choices:
ATI FireGL V3100 (PCI-Express), ATI FireGL V5100 (PCI-Express), NVIDIA NVS 280 (PCI), NVIDIA NVS 285 (PCI-Express), NVIDIA Quadro FX540 (PCI-Express), NVIDIA Quadro FX1400 (PCI-Express) or NVIDIA Quadro FX3450 (PCI-Express)
HPxw8200 Workstation

OS
Microsoft® Windows® XP Professional
Processor
(1) or (2) Intel® Xeon™ Processor 2.8GHz, 3.0GHz, 3.2GHz, 3.4GHz, 3.6GHz or 3.8GHz
Memory
16GB (For greater than 4GB memory support, a 64-bit operating system is required)
I/O slots
2 PCI, 1 PCI Express x4 (x8 connector), 2 PCI-X (1 x 100MHz, 1 x 133MHz), 1 PCI-Express x16 graphics
Drive Controllers
Integrated dual channel SATA/150 controller with RAID (0 or 1) capability; integrated dual channel Ultra320 SCSI controller with RAID (0, 1) capability
Storage Bays
8 bays - (3) external 5.25", (5) internal 3.5"
I/O ports
1 x Serial port, 1 x Parallel port, 2 x IEEE 1394 ports (1 front, 1 rear), 8 x USB 2.0 ports (2 front, 6 rear)
Removable Storage
48X CD-ROM, 16X DVD-ROM, 48X CD-RW, 48X DVD/CD-RW Combo or 16X LightScribe Dual Layer DVD±RW/±R
Supported leadership graphics Card Choices
ATI FireGL V3100 (PCI-Express), ATI FireGL V5100 (PCI-Express), NVIDIA NVS 280 (PCI), NVIDIA NVS 285 (PCI-Express), NVIDIA Quadro FX540 (PCI-Express), NVIDIA Quadro FX1400 (PCI-Express), NVIDIA Quadro FX3450 (PCI-Express) or NVIDIA Quadro FX4500 (PCI-Express)
HP xw9300 Workstation

OS
Microsoft® Windows® XP Professional SP2
Processor
(1) or (2) AMD Opteron™ 200 series processors 246 (2.0GHz), 248 (2.2GHz), 250 (2.4GHz), 252 (2.6GHz), 254 (2.8GHz); dual core processors 270 (2.0GHz), 275 (2.2GHz), 280 (2.4GHz) with AMD64 Technology & AMD HyperTransport™
Memory
32GB (For greater than 4GB memory support, a 64-bit operating system is required and must have Dual Processor)
I/O Slots
1 PCI (full-length), 3 PCI-X (full-height; 2 x 100MHz, 1 x 133MHz), 2 PCI Express x16 graphics
Drive Controllers
Integrated four-channel SATA-II controller with RAID (0, 1 or 0+1) capability, integrated dual channel channel Ultra320 SCSI controller with optional external connector
Storage Bays
8 bays - (3) external 5.25", (5) internal 3.5"
I/O Ports
1 x Serial port, 2 x IEEE 1394 ports (1 front, 1 rear), 1 x PS/2 keyboard, 1 x PS/2 mouse, 6 x USB 2.0 ports (2 front, 4 rear), 1 x RJ-45 Network, 5 x audio ports (front: headphone and microphone; rear: audio-in, audio-out, mic-in)
Removable Storage
48X CD-ROM, 16X DVD-ROM, 48X CD-RW, 48X DVD/CD-RW Combo or 16X LightScribe Dual Layer DVD±RW/±R
Supported leadership graphics cards choices
NVIDIA Quadro NVS 285 (PCI-Express), NVIDIA Quadro FX 540, NVIDIA Quadro FX 1400, NVIDIA Quadro FX 3450 (PCI-Express) or NVIDIA Quadro FX 4500 (PCI-Express)