Are you using a Tablet PC? You can convert handwriting to text only if the
handwriting was created on a Tablet PC, because only the Tablet PC system has
the recognition capability and it stores the recognized text with the
handwriting.
If you are using a Tablet PC, but the command is still not available, you
can try this:
Select the ink and click Tools > Treat Selected Ink As > Handwriting. Then
try selecting and converting it to text. If you have OneNote 2007 Beta 2,
make sure that you are using the command in Tools > Convert Handwriting to
Text. The command is no longer available on the context menu.