You don't actually need software to get your router running. Using the web-based setup page is often faster and more reliable. Step 1: Physical Connections Linksys E900 - Download - Softpedia
If you have lost your original installation disc, you can find official software and documentation online. linksys e900 setup download
This is the desktop utility used for initial setup. You can download the Linksys E900 1.5 Build for Windows directly from repositories like Softpedia or find the original CD image on the Internet Archive . You don't actually need software to get your router running