I'm right there with you.
I'm on a roll today...downhill, at an 85 degree angle.
Here's where I am:
crystal.tar.gz unpacked and untarred in one of my $home subdirectories.
When I use KDE Control Center-->Appearance&Themes-->Icons to try to 'Install New Theme,' I choose */index.desktop, I get 'The file is not a valid icon theme archive!' However, it's the only thing I can highlight and select, TTBOMK.
Can anyone help?