Since I have to work with (/&%$ยง"! Vista on my new PC, ddsconverter doesnt work anymore.
I found this alternative:
http://www.brothersoft.com/dxtbmp-71327.html which works surprisingly good.
You cant convert batch files and you cant convert to .jpg but personally I preferred .tga anyway. Whats more you can have a fullscreen window and check the textures in 100% or more resolution instead of that tiny image from dds.converter. AND it has some easy usable functions for alpha channels.
I have worked for some hours with it now and so far I can only recommend this one.
In case you find my grammar and spelling weird ---> native German speaker ^^