I installed the recommended IDE --> mSATA adapter and a Samsung 250 GB mSATA SSD in my Mac Mini and so far it works great. The speed difference is noticable, even though it would probably be much faster on modern hardware.

The only downside is that there are no screws to keep it fixed in the slot, so it relies on the pins. But they are sturdy so I don't expect much problems.

Thanks everybody for the help!