It isn't hard to install a new drive. There are three thumbscrews to remove the case, two screws (need phillips head screwdriver) to remove the drive bay, and the usual four screws for the drive. Space may be tight for some....but it performs very well.
There is a new style of case that has been redesigned for tool-less assembly, more HDD space (you can fit 3). It also has more efficient cooling and lower noise.
The Shuttle I have cannot be upgraded to the newest style of components....no DDR2, PCI-X or Prescott processors. The new "P" chassis allows for those.
Back on topic.