automan has got a standard IDE HDD working with the PSTwo v12 console. Up until now, the only way of accomplishing this was through the upcoming (in final debug stage now, release pending) USB-Loader using an external USB HDD. Although quite vague, according to automan his method is is done "via a combination of hardware and software modifications."
However, automan also states that "it is not released yet, nor it will not be publically released in future. If we ever see this method to be available, it will be done either by a team that will join me in order to manufacture this discovery, or by someone kind enough to develop a free solution for all us PSTwo owners.http://www.ps2ownz.com/v12_hdd_proof-of-work.jpg