Ihave tried it, but obviously it didn't work with my printer (HP 650 C), the ink just didn't dry well.
However, the better way to use them would be designing your decals, printing them on regular paper and then go with your design and you blank decalpaper to a copycenter, and then copy your design to the decalpaper.
Keep in mind that you can not print white (unless you've got an ALPS) so you have two kinds of that decal paper available ; "white" and "transparant".
Oh, almost forgot ; after you have your design on the decalpaper you need to seal it with liquid decal, avalable from (amongst others) MicroScale.