Is there a built-in text-to-graphic utility for OS X Lion?
ImageMagick doesn't come with OS X, but it should though.
convert -background skyblue -border 10 -bordercolor skyblue -fill 'hsb(10%,50%,50%)' -font /Library/Fonts/Arial\ Narrow.ttf -pointsize 24 label:"some text" output.png
If you have to specify some more complex styles, using webkit2png might be easier.
echo "<style>em {padding:5px}</style><em>Test</em>" > test.html
webkit2png test.html --clipwidth=55 --clipheight=35 --scale 1 -C