When I installed Slackware 64 I fired up gimp I could only open/save the native XCF files. I googled for a while with no luck. I downloaded the latest stable source (and required dependencies) and built with src2pkg (this lets you build multi-core support BTW). I installed the new pkg and still had the same problem. More googling still turned up nothing. I turned to the #gimp channel on irc, where they were convinced that src2pkg was a useless script and I should just build it manually. I knew that there had to be something simple I was missing.
The Solution:
The plugins that handle opening / saving other files types are plugins. Slackware installs the defualt plugins to
Code:
/usr/lib64/gimp/2.0/plug-ins
This is not where GIMP is looking for them. You have to tell GIMP to look there by adding that location to the Edit->Preferences->Folders->Plugins page.
Modules, Interpreters and Environment seem to handle this on their own, but the plug-ins do not.
Hope this helps someone.
Eric