When Sony releases the Internet pack it will have an interface for a IDE hard drive. What the exact specs will be is not yet known.
I believe if you get the PS2 linux kit it comes with the interface, or perhaps even a HD
If you look on the back of the PS2, there is an open bay for a HDD to be put into. If you have just the HDD, it goes in the bay and the thing that covers the slot goes back on to hold it in. If you have the modem, it goes in place of the cover. If you have both, the modem is the thing that holds the HDD inside.
But there are no HDDs for the PS2 for games available yet.
Only if the game was programmed to do that, and so far the answer is no.
Sony loves their memory card business, lots of easy fast cash, so I wouldn't expect them to push developers to that.
The HD in the PS2 is mostly to be used for Sony's plan that instead of going out and buying a game that we just download it to our HD.....great idea, not! I love to have the ability to touch and look at the case and the manual, etc...nothing is better than going out and picking up that game you have been waiting on to come out. I for one will not buy into this downloadable games bit.
I own the HDD that works with the PS2 Linux kit. The HDD is currently a proprietary hard drive. I wrote an article for Gaming Age on the PS2 Linux Kit if you want some info on it: Link Removed
The Sony commercial HDD (to be used for games) comes with a utility disc in Japan that allowed folks to partition the 40GB HD to support both PS2Linux and PS2 games.