An inelegant solution for a fairly short document is to use the Snipping Tool for Tablet PC (http://www.microsoft.com/windowsxp/t.../powertoys.asp) to clip and paste the Acrobat pages into a Word Document. You can then use Word's pen to annotate the document.
If you have Acrobat, you can then convert it back to *.pdf. If you don't have Acrobat, you might want to try pdf995 to do the conversion (download from http://www.software995.com). The free version hurls you to the software995 website after each conversion, which is no big deal. Or you can pay $9,95 for a license.
I hope that helps.