I've had a LOT of good luck making my own panoramic skies (regular 8-Bit TIF images and even JPEGs - not 16-Bit) and using them as environment mapped skies. I take a series of shots across either ALMOST an entire 360 degree view (or even 180 works pretty well in some cases), to an ACTUAL 360 degrees and assembly them in PS - NOT HDRI imaging, but just making a general panoramic.

Believe it or not, the environmental lighting for just 8-Bit images works REALLY well in Vue5Inf (can't vouch for any of the lower versions).

When importing an image, since it's just a sky, when ckeck the box tomake sure it only applies to the top half of the environment - no stretching! This sounds like your problem described above.

Good luck - hope this helps!
-Lew ;-)