Here are few links worth trying when you start your adventure with Gimp:
GimpDome
-helpful people, loads of tutorials to read and friendly atmosphere
Gimp Paint Studio
-Ramon Miranda's great addition to Gimp- set of brushes, tool presets and color palletes to make painting more efficient and effective- must have for starter painters! In the article you'll find link to his blog- take some time to explore it, his artwork is simply astonishing :)
Current version of plugin is 1.07 and what's interesting, mr Miranda is working on new, polished version of his creation. You can see further details here:
Oil Presets
Pencil Presets