I don't know anything about growing them from seeds, but those stupid little cacti you see in grocery stores, that have the green base with the orange/red/purple/yellow cacti grafted on top of them are dragon fruit-growing cacti. If you can't get the seeds to work, you could always buy one and knock the graft off somehow.

http://plantsarethestrangestpeople.blogspot.com/2008/01/unsung-hero-hylocereus-undatus.html

Hi
i grow several types of the so called "jungle cactus"
The true 'Dragon fruit" is Hylocereus guatamalensis.
Look up epicactus if you don't have a latin name.
There are hundreds if not thousand in these families.
Can't be of much help with culture as I grow it outdoors.
It is a semi epiphytic vine. Mine never flowered nor fruited before getting over 10 feet tall it is of vine habit.. Have no experience with seed as these are incredibly easy to start from cuttings.
I would suggest maybe a cactus mix .it must be well draining because about the only thing that happens to them is rot from too much water.
These families have some of the worlds most spectacular flowers .You're in for a treat lol gary

i just purchased a rooted 4inch cutting of the yellow variety dragon fruit b/c i heard they're fruit is much sweeter, is this true or is this just another gimic. i am also wondering how long it will take to bear fruit. I will be growing this indoors by a window because i live in pennsylvania, i will also be setting up a growing light,is there a specific setup i should use? I heard that the yellow varieties are self fertile and set fruit on their own, this is especially important because it will be grown indoors, is that true. I bought it online and i cannot get any info out of the person i bought it from. This is my first fruit plant that i am trying to grow and any help that you could give to help this experiance be a pleasurable one will be greatly appreciated. Thank You