Well taking them apart will VOID any warranty you may have on them, even you you've boughten the iPod extended warranty. Why do you want to take it apart? If you want to see whats inside it, there are TONS of site on the web that show both the 4G iPod AND the iPodmini taken apart.
The safest way to take them apart is to take them to your local Apple Certified Service Center and have them do it.