According to the Engineering Plan on our Technical Support website, the first version of PI WebParts that will be compatible with SharePoint 2010 is version 4 - this is planned for the second half of 2010. This is also the version in which we will migrate from the Adobe SVG technology to Microsoft Silverlight, to render the web parts.
You will also hear more about the joint OSIsoft|Microsoft roadmap in one of the closing keynotes at the OSIsoft vCampus Live! event.
You might already be aware of this, but just a quick note on the fact that migrating from a 32-bit (x86) installation of SharePoint 2007 to SharePoint 2010, may involve more than just updating the version of SharePoint and PI WebParts... SharePoint 2010 only comes in a 64-bit version so you need to make sure you are on an x64 system.