Most of the HP workstations I work with do not offer "AHCI" as an isolated BIOS setting. Rather, AHCI is included in the advised setting. Both the BIOS settings of "RAID + AHCI" or "RAID" result in getting both the RAID and also the AHCI drivers installed.
That is how HP sends them from the factory, and that is the recommendation of Intel. You may never ever plan to use RAID, but that is the recommendatin. You'll get AHCI drivers included unless you choose the IDE setting.
There are some circumstances where I need to drop down to an IDE Separate setting to accomplish some odd project, but I always attach a post-it note to remind myself to reset BIOS back to "RAID + AHCI".
In XP if you did not have BIOS set to that before a clean OS install you would be stuck. With W7 and above if your BIOS settings were set to IDE during the OS install you'd at least have a method to layer them in later. It's all in here......
Remember to do your install correctly so you get the special "system reserved" small partition installed along with the main W7Pro64 install. Also, if you get that taken care of before the end of this month you should W10Pro64 activate your workstation for free. Even if it is a stunt quick and dirty W7Pro64 activated install make sure to not lose out on that 200.00 savings. Your UUID will then be registered at MS and you'll be able to shift over to W10 anytime in the future.