Yes, you likely can.
All of Ubuntu's variants allow installing from the media created from downloaded images. It may be helpful/required to have an Internet connection as any of the latest security updates will be installed at install time at the least; if not all of the new system's packages.
And it's not required to remove Win7. If you have the room to spare on Win7's partition, do that (Windows 7's Disk Management component will allow you as long as you meet it's conditions), and you can "dual boot", that is have both Windows and Ubuntu available on your desktop.
Last edited by goumba; 05-13-2013 at 06:21 AM.
Reason: I missed the X in Xubuntu