I'm not sure if it will fit in the Antec 300, but it should, though you might have to remove the hard drive cage
However, the Rosewill Challenger will fit anything out there if you remove the middle hard drive cage -- we saw that in the tom's hardware article.
Being that this will be my first build I don't know exactly how you can take these apart... In the 300 for instance i can just remove one of the hard drive cages and that should free up the room?
I dont plan on installing any additional HD's. Just the one... MAYBE a SSD down the road.