You may not need to upgrade Quickbooks just to run on Windows 7

If you have problems with specific features of Quickbooks after upgrading to Windows 7, first try running Quickbooks in Windows XP Compatibility mode. You can set the compatibility mode by right-clicking your Quickbooks icon, selecting properties, then the Compatibility tab. Then click the “Run the program in compatibility mode for” checkbox and choose Windows XP (Service Pack 3) from the dropdown.
I did this and it solve the problem I had trying to send an invoice where I get error -20 from the Quickbooks PDF Converter in Quickbooks Pro 2007.