Great article for fixing pre upgrade related issues:

http://sharepointreporter.wordpress.com/2010/07/30/fix-pre-upgrade-check-errors/

One thing to add.  Use the query here to find the name of the pages that contain the offending webparts.  I thought deleting the page would make them go away, but I was wrong.  I had to recover the pages that I deleted from the recycle bin and then open them in web part maintenance view (appending “?contents=1” to the url and then delete the webparts from the page.   http://surfpointtech.com/2012/06/28/how-to-find-a-sharepoint-webpart-name-from-the-id-or-guid/

 Here’s the STSADM commands:

STSADM -o preupgradecheck

and this one to find the sites that the webparts live in:

stsadm -o enumallwebs -includewebparts > i:tempwebparts.txt

Better yet, use the SQL command above to get the actual page that the webpart lives in.