Labelling a map with Gimp

[Mouse]

What do you mean 'lower or raise' text?

If you're trying to do stuff you would do in a vector programme it won't work. You have to do it the GIMP way. ie move the text box, or edit the path till its in the right place.

EDIT: if you mean use it like a word processor with subscript or superscript letters, it just won't hack it. You would need to export your map at full size and open it in Inkscape to do stranger things than just bend your labels around a curve

(That's what I've heard about Inkscape. I've never really put it to the test, so someone else would have to help you with that)