Glad to help a fellow Linux user (even if I'm on Slackware).
I read the source code of the program, really skinny, and I see that the syntax required is
ttt [-?] [-u] [-f /some/file.ttf] 'The Text' > file.ngc
ttt_dxf [-?] [-u] [-f /some/file.ttf] 'The Text' > file.dxf
There is also an undocumented -d parameter for debug.
The default font used is /usr/share/fonts/truetype/ttf-bitstream-vera/VeraBI.ttf.
If you don't have it in that path you can locate the VeraBI.ttf(¹) file on your system and create a symlink (no need to physically copy the file).
As you can see, you have to call fonts by file name rather than TTF name, so this could be a bit odd (but in this way you don't need to install thousand of "fancy" - and almost useless - fonts). GIMP deals better with uninstalled fonts: at least you can see the TTF name.
The drawback of this program is you have to use the same font for the whole text, but you can use the minimal graphic set included in some Unicode fonts.
If you want to have something more complex there is a G-code extension for Inkscape. It is discussed in this thread:
http://www.cnczone.com/forums/showth...light=inkscape (New export to Gcode plug-in for Inkscape)
For thousands of fonts, even GPLed or free, see http://www.dafont.com - and don't forget to browse the dingbats section: often the right dingbat can save you a lot of drawing time.
(¹) a user told me he couldn't find the file with the name in Courier face: his file name was in Arial, so he wasn't sure it was the good one.