thanks snake
another possibility is using the photoshop plugin from nvidia:
Adobe Photoshop Plug-ins
dunno if there is a support for paint shop pro or gimp, but for the (pc) photoshop guys it's a nice tool.
just for viewing them you can also use Irfan view (freeware).
in most cases you don't need to do the convertion into dds files, because the game engine also supports *.tgas for texturing.