Grab the .DDS plugin from the nVidia website - works in Photoshop and PaintShopPro5+.
It's all you'll ever need for DDS (Direct Draw Surface) files. In case your wondering why they'd opt for those, they use less memory when loading, load directly into video ram, allow custom mip maps, and support alpha transparency - they're mostly used as a final format, like when you'd finished with a texture, make a .DDS version and use that - but still use a .BMP or something while working on it. It's not ideal to load a .DDS too much, the weird setup they often have can be a pain, like having to grab your actual image from a bed of mip maps - basically smaller versions of your texture to speed up realtime texture scaling (helps performance).
Van-B
Put away, those fiery biscuits!