What hard drive can I replace for my defect iPod

Hi

My Ipod Classic 160gb has suddenly got a problem , the RED X is appearing when trying to start up the Ipod, and it's making strange noises.

I've read on the web, that this means the hard drive has to be replaced.

So here's my question:

Can I replace a hard drive that is made for earlier models of the Ipod? Is it possible to replace it with a 30gb hard drive (that is actually made for earlier Ipod generations)??

(My Ipod generation is 7th Gen)

I'm not really interested to pay for a 160gb hard drive that is over $100, that's why I would buy a cheaper one with less capacity.

Thanks in advance

Sara