Windows and Mac users do not need to download and install the Qt libraries - these are provided in the installers as the necessary dlls or frameworks. Linux users will need to install at least Qt 4.2, but most major distributions should have it installed already.
Example model files are provided and installed (in the RPMs) and are used in some of the tutorials. The OPLS-AA, UFF, and Canongia-Lopes (ionic liquids) forcefields are also included, but please note that the OPLS-AA is a big forcefield and is missing automatic typing descriptions for a number of atom types (all parameter data is present, however). If you find yourself filling some of these in, don't hesitate to send them to me! Similarly, if you implement a forcefield, or wish some other intra/intermolecular potential functions to be included in Aten, write me an email - I'm more than happy to expand this part of the code.
If you see the following message when trying to run the program...
...(or something along the lines of a missing DLL entitled "msvcr80.dll") then you will need to install the some extra run-time libraries from Microsoft (only 2.5 MB). If the preceeding link is dead, Google "Microsoft Visual C++ 2005 SP1 Redistributable"). Note that it since the packaged version of Aten is compiled with Visual Studio 2005 SP1, the Redistributable package must be the SP1 version as well.