The hard drive for IPS-11G should be externally powered so that the power needed would not be drained from the IPS-11G unit. The size of the hard drive is recommended to be less than 250G so that the file structure of the hard drive will not overload the built-in memory of IPS-11G unit when connected.
We have in our office 160G and 250G hard drives that can be made external with iMicro external cases. The problem of compatibility does not come from hard drives but from the external cases. Finding a right case can be difficult and that is why we only use one type of iMicro cases which we tested (this does not mean all iMicro cases will work).
Please read the User's Manual of IPS-11G for the limitation on the number song files that can be loaded in a hard drive for play.