Yes, Windows 7 will let you choose a partition to install itself into during the installation procedure. Simply choose your current Windows partition.
However, the Windows installation procedure will overwrite your MBR where grub is installed. This means that you will not be able to boot into your Linux system after the Windows installation; your PC will always boot Windows. Don't worry, though. Your Linux is still there, you're simply missing the option to boot it. All you will have to do at that point is use an Ubuntu Live CD or USB, and reinstall grub using a tool such as
BootRepair. This will enable you to dual-boot again.
See here for instructions on how to repair your dual-boot functionality using an Ubuntu Live system.