If you want to convert your model textures to DDS read on.

Maybe it helps, it will only work if your models have external textures.
Even better: External textures with the same filetype, for example 24 bit tga.

Make a backup
Use "HexEditor NEO" to search and replace "tga" or "pcx" or "bmp" in the mdl files with "dds". You can do it in a batch process.
Convert your model textures to DDS.
Copy them into the model folder.
Voila.