I'm guessing it's a micro-ATX system so you would need a case that supports that specification. If it's an mini-ITX you'd need a case that supports that. You can usually tell by the number of expansion slots on the back or by looking at the motherboard.
You may also need a new power supply if the current one doesn't fit easily in the new case.
One other thing to be careful of is any proprietary connections that they use.