The system requirements for Publisher 2010 on http://www7.buyoffice.microsoft.com/usa/product.aspx?sku=10234421&cache=-1905222315&culture=en-us don't say anything about Office 2010 being installed as a prerequisite. But if you find it isn't possible to install it when you only have Office 2007 I have to believe you (didn't try). What is the exact error message, by the way? I don't think it is "I can not add myself to your existing 2007?? version."
Installing the Office 2010 trial would be another option, but I wouldn't recommend that if you have a working and satisfactory 2007 version at theis same computer.