Most landsat data is distributed as separate TIFF files for each band with an associated metadata file '_mtl.txt'.  ENVI 4.7 can now read the metadata file and open the separate TIFF files together as a single file and assign appropriate band names and wavelengths to each band.  There is also a patch for ENVI 4.6 that would provide this functionality.  You will need to contact Technical Support to acquire this patch.

I am trying to do the same thing in an IDL script. I need to calibrate Landsat 7 data to radiometric quantities. I know that TMCAL_DOIT will do the process but I would rather not read the header file and input all the necessary information myself. I tried to use ENVI_OPEN_DATA_FILE and ENVI_OPEN_FILE. Both give no popup envi error as long as I give it the right file name (Using the _MTL.txt file). but the fid is -1. Not sure what is going on. Should I be using IDL scripts to be reading in the text and assigning variable names manually? that seems like a lot of work to read a header file which ENVI can already read. Thanks