Before you go buying a swap magic disc, are you familiar at all with ESR? I used it to play both Kingdom Hearts games that don't run from HDLoader. You just patch your ISO then burn your backup, load ESR from Free Memory Card Boot and it plays. There are two versions of the ESR ELF file, one that stays memory resident and one that doesn't. Some games work with one and some with the other. The basic concept is that it adds a couple empty files to the disc so that the PS2 reads it and thinks it's a DVD movie so it doesn't reject it as an invalid disk, then when you run ESR it loads it as a game anyway.
As far as which version PS2 to buy, I always recommend a fat PS2 over a slim, because HDLoader from an internal HD is compatible with way more games than USB Advance with a USB hard drive, so slims are kinda a no-no for hard drives. They sell kits for the older slims that allow you to hook up an internal hard drive, because the IDE pinouts are still on the motherboard, but that involves a lot of soldering, and the nice HD Combo kits that replace the bottom of your slim's case to hold an internal hard drive are no longer made and impossible to find.
Then as far as which fat version to get, I usually say get one of the later versions of the fat. There's an older one, and I think it may be the v4 (scph 30001), but don't quote me on that, I can't remember, but whatever version it is, I have it tucked away in my closet because I bought a newer version. Anyway, I went to play one of the Metal Gear games and it just wouldn't work. I searched all over the internet to finally find out that it didn't work with one specific version of PS2. I don't know if there are any other games that do that, but now I'm using a v7 PS2 and loving it.
