I figured out that Hal's hard drive is not SATA, but SAS (Serial Attached SCSI, see: http://en.wikipedia.org/wiki/Serial_Attached_SCSI). The existing HDD is a Maxtor Atlas 10k5 073SAS.
I didn't know this technology before. Since there has several flavours of connectors for SAS, I think we should ask Dell for the proper hardware to buy. Also note that the wiki page says that second generation SATA drives can be connected to SAS buses.
What's exactly the model number of Hal ?
Sébastien