This link provides the steps you need to take to upgrade InfoPath forms from 2007 to 2010:
How many forms do you have that needs to migrate from 2007 to 2010?
You can also open the 2007 forms in Designer mode of InfoPath 2010, save as 2010 filler or browser.
You need to make sure data connections are updated to point to new sites/document libraries/lists etc.
Any custom code that may contain data connections should be updated.
Inspect Rule Inspector to see if you find any connections hardcoded anywhere.
We migrated a couple of Admininstrator Approved 2007 InfoPath forms to 2010 SharePoint, and all of a sudden there is a Data Connections library in SharePoint 2010. I cannot find any data connections in InfoPath designer for those forms. There is only one Data Connection in InfoPath designer, and it is the Main Submit.
Where do I find the Data Connections that show up in SharePoint 2010, Data Connections library in InfoPath Designer?