Yes, it will read drives bigger than 4GB. There are people that use them with 40GB+ hard drives. Only real problem is it can take forever to read in all the files before it starts playing (30 seconds - several minutes).
The only real limit that I know of with them is it can't handle more than 15,000 files. Search around a bit more on the net and you can find out how to configure a larger drive to use with it.