I've got that right now. It just depends on how many places you have to plug it in. Not just on the motherboard, but on your power supply. That was my bottleneck for a while, limiting my ability to add on drives, but I got a new one with plenty of power cables for the hard drives. Also you need to consider how much space you have in your case. If you mix the SATA drives with the IDE ones and you still have enough physical bays and power cables for it you can fit even more drives. This tends to happen if you've just been aquiring drives as you go along.
If your mobo has 2 SATA ports, you'll be able to put 4 devices on that. Do you have some drives already or are you buying all new?
here are a couple of suggestions
4x 320gb drives for a rounded total of 1280gb
$99 each, $396 total
3x 400gb drives for a rounded total of 1200gb
$139 each, $417 total
Both of these scenarios will get you at least 1TB, but I'm not mathy enough to do the figuring on how much it *really* is. Personally I'd go with the 400gb setup. It will take up less space and you'll have more opportunity to expand if you need more capacity later.