I assume the area between the black lines is white. Have you tried to select it and a.)
colour to alpha it? Oh and make sure your graphic has an b.) alpha channel.
a.)
![Image](http://gimpchat.com/files/1831_Colour%20to%20alpha.png)
b.)
![Image](http://gimpchat.com/files/1831_Add%20alpha%20channel.png)
Right click on your picture and if it has "remove alpha channel", it has an alpha channel. If not then you need to add an alpha channel.
It can be done with other colours as well but you have to be precise in the colour you want to remove or you will not remove all of the colour you wish to remove.
Just thought of another idea
You could use a couple of paths but you would have to stroke them separately. Put a new transparent layer over your letter. A path over that layer on the letter then stroke it black. Depending on the size of your graphic would depend on the size of your stroke.
Do the same again with another transparent layer do another path, and stroke. after you can merge all visible layers. Don't "flatten" unless you want the background your gimp's background colour. Export as a png and this will keep the transparency.