I started by opening up the T5700 and removing the flash module. I then connected the 44-pin IDE cable to the motherboard (Figure 6).
Figure 6: HP T5700, cover open with 2.5" IDE drive installed
Be careful to note the location of pin 1 on the header and the red stripe on the ribbon cable (Figure 7). Unlike larger IDE connectors, the laptop-sized header is not keyed, so the cable can be connected in reverse, with possibly tragic consequences.
Figure 7: Closeup of the IDE cable connecting to the T5700 motherboard
The hard drive is mounted by simply taking advantage of the holes in the metal portion of the expansion chassis. The mounting holes in the drive are not on the same spacing as the holes in the chassis. So just rotate the drive until two of it mounting holes line up with two holes in the sheet metal (Figure 8). Two screws are adequate to mount the drive. If you feel it needs to be more secure, you could always lash the drive into place with nylon cable ties.
Figure 8: T5700 expansion side showing HD mounted by 2 screws
If you're not using the T5700 expansion chassis, then the drive will still fit. But you'll need to be careful to locate it so that it doesn't interfere with any of the heat sinks or connectors on the T5700 motherboard when the case is closed.
New models in the HP thin client family have faster CPUs and larger internal heatsinks. This makes mounting the drive a little trickier, but it can still be made to fit nicely into the standard chassis. However, the normal chassis side is a solid sheet of metal, so you can simply drill four holes to mount the drive in the desired location.
Figure 9: Rear view of the T5700 with the expansion side added
When using the expansion chassis, you need to install a filler blank in the back where the PCI card would normally reside (Figure 9). This will keep the system from accumulating dust internally.
Figure 10: T5700 with and without the expansion chassis
It's also worth mentioning that HP does not intend the T5700 to run while sitting horizontally. They provide the little stand for a reason—cooling. The basic chassis is designed to cool properly when oriented vertically. The extra perforations in the expansion chassis reduce cooling issues to a degree. But I still prefer to stand the unit vertically.