Thanks Valkrionn, tesb and Selphi for the help so far. Two things still:
1. I grabbed a couple unique features from Orbis, including the .nif art. Both have display problems on the map. One has a pink "floor" (the feature itself is fine), the other is totally pink (can still see the outline of the feature, but it is all pink). Do you have any suggestions for how to fix this? (and what program to use?)
2. I'm using paint.net to open and re-save the unique feature icons as promotion buttons. I still have big pink squares on the mouse-over. I followed Selphi's instructions but there are additional settings which may be wrong. The full set I used was:
DXT3 (Explicit Alpha)
Compressor Type: Cluster fit (Slow/HQ) ...the other 2 options are Range fit and Iterative fit
Error Metric: Perceptual ...other option is Uniform
Weight Color By Alpha (unchecked)
Generate Mip Maps (checked)
Super Sampling (this is resizing method; shouldn't matter)
The images are 64x64. Are any of my additional settings wrong? (I guess I could try every possible combination, but it's easier to ask.)