The DDS Converter 2:
http://filebeam.com/8bbdf4017ad707fd673900f2e38d1bb4Please PM me if anything is wrong with it.
How it works:
First you need WinRAR to unpack it.
Google it, it's easy to find.
Then rightclick the converter (when it's still a .rar) and click Extract Here.
Then a folder called DDS Converter 2 will be created. Open it and you'll see DDS Converter 2.exe. Open that. Then if you want to extract a .png image to .dds, look at the bottom of the DDS Converter. It says: Output format : *now you can choose what*. If you want .png to .dds click search for your .png, highlight it, and put Output format to .dds. Then press convert and your .png changes into .dds =).
.dds to .png is exactly the same. Highlight your .dds, change output format to .png and convert =).
Also I pmed this to you xP. Maybe more people wanted to know.