Please confirm that you are doing the following:
1. Download the latest version of NodeXL from
http://nodexl.codeplex.com/releases. The version number changes regularly, but as of today it's 188.8.131.52.
2. Unzip the downloaded Zip file into any folder. Use WinZip or a similar program, or just right-click the Zip file in Windows Explorer and select "Extract All."
3. Close Excel if it's open.
4. Double-click the file called Setup.exe. Do not double-click the file called DoNotUseThis.msi. Double-clicking DoNotUseThis.msi is the one way I know of that you can get the "Please install Microsoft Office 2007 before installing this