Please do the following:
1. Download the latest NodeXL setup program from
http://nodexl.codeplex.com/releases and save it in some folder on your computer. It's a Zip file with a file name something like NodeXL_1.0.1.xxx.zip.
2. In Windows Explorer, navigate to the folder where you downloaded the Zip file.
3. Right-click the Zip file and select "Extract All" from the right-click menu.
4. In the "Extract..." dialog box that pops up, accept the folder that Windows suggests, and make sure that "Show extracted files when complete" is checked.
5. Click Extract.
6. Another Explorer window will pop up. One of the files in this window is called Setup.exe. Double-click it to install NodeXL.