Verified answer

If I'm not mistaken, the Dimension 2400 doesn't have any SATA connectors. Therefore, you would have to add a PCI SATA card.

However, PCI SATA is not as fast or efficient as SATA that's integrated on the motherboard. So I recommend you skip SATA and hunt for an IDE hard drive instead.

Keep in mind too that Dell doesn't usually give extra brackets in their cases for you to mount additional hard drives. There is a spot for one, but you'll need to order an additional bracket most likely (look on eBay for good prices). Also be sure to look up your specs in your manual, or go out to Dell's site if you need to download a copy. They have a scanning tool as well that will show you what's in your system now. Make sure what you're looking to buy will be compatible.

For the hard drive, consider shopping at http://www.newegg.com/ or http://www.pricewatch.com/

As long as you can make it fit in the case......