All the uu-encoded gz-compressed files were prepared with the uufiles utility. The header of those files explains very well how to extract the data, once the file has been saved to disk. If you are on a unix machine these files will unpack themselves: save the file to disk, calling it, say atlas.uu, then type: csh atlas.uu.
  The format can't be any easier, this file has two columns: wavelength (Å) and normalized flux (relative to the local continuum).
  Once extracted, the Flexible Image Transport System file can be read from IRAF  or IDL  (e.g. using mrdfits.pro: IDL> d=mrdfits('atlas.fits'). Note that the image has two layers, the first one contains the vector of wavelengths (Å) and the second one the normalized flux.
  Once extracted, the Flexible Image Transport System file can be read and manipulated in IRAF  very conveniently, as the dispersion has been interpolated to a constant step, which is specified in the header. Keep in mind that nobody has checked for a possible loss of accuracy in the interpolation, which was done with the IRAF task rspectext.
  Once extracted, the eXternal Data Representation file can be read from IDL as follows:

IDL> openu,1,'atlas.xdr' & d=dblarr(2,122504) & readu,1,d