A GNU C# compiler can be found as part of the Mono project, you can find a package in the VectorLinux GSB repository. The GSB repo is kind of experimental, so I suggest you to deal with it carefully. The dependency information is wrong, so use the -s flag to test what is going to be installed. Gnome is built in a peculiar way, in general the applications are known to work only if compiled against a very specific version number of its dependencies. The GSB repo hosts gnome 2.24 iirc, so stick with the versions for that gnome release. IIRC there is a F-spot package there and it should work if you install all the deps, check the Gnome docs to find out what are they.
Sorry if the post is a bit confusing, the topic is proportionally complex