New computer case

So I bought a prebuilt computer and I know that is not the best idea but is was a great deal at the time. But the case doesn't have much room and I have always been worried about heat, I am pretty sure that thats what broke why previos 8800GTS. Now I want to install some more hard drives, but there is no room. So I was wondering if it would be possible to take the motherboard and all the components and install them into a new case. I have read that hp makes its motherboards so that they only fit into their specific cases. Is that true? My motherboard is an Asus P5BW-LA, if that helps at all. Also, I want to put that into something like the Antec Nine Hundred or A Thermaltake Armor-MX case, or some other cool case, would that be possible? Thanks in advance

I am kind of looking for the mid tower case I won't need that much room. Good case and deadcell did the back I/O panel shield of the motherboard fit into the case? Also, anyone know the best cases under $100?

The best cases under 100 USD would be the Antec 900 you were looking at, the 900 II or one of my personal favorites, Thermaltake V9 Black Edition. I am sorry, I guess I am not too familiar with mid towers. I haven't tried the 1200 yet. In time I shall see. They should realy just classify all factory MOBOs in 3 different universal sizes. No odd balls, and built cases that supports all sizes. Just a suggestion, you know! Good luck with the transfering process! Let me know how it went...

I liked the looks of the V9 from the iBuyPOWER builder but I too am leary. After lots of research I'm leaning towards the Cooler Master Storm Sniper.