These are .RAW texture files for use with PalMod. You can load them using the File :: Load Texture option in the Preview window. The "Flipped" version is for old versions of PalMod. Current PalMod (1.73 and newer) uses right-side-up RAW files, so "PalMod1.22Previews.rar" will work great with that.

There's a guide on the main site for making your own previews if you want to do that.

      Name                    Last modified      Size  Description
      Parent Directory                             -   
      sample-textures.rar     2021-09-09 11:47   32K  A few sprites
      palmod_eidrian.zip      2020-02-11 23:18   18M  MvC2 dev sprites
      PalMod1.22Previews.rar  2021-09-09 21:27  1.0M  Old previews
      PalMod1.22FlippedPre..> 2021-09-09 21:27  1.0M  Old previews (flipped)
      ExtraSettings.rar       2020-06-11 15:15  1.0K  pointless settings