This old question says how to reinstall Windows 7 from DVD without messing up the Ubuntu partition:
How do I reinstall Windows 7 while keeping my dual boot configuration?
However, I have a Dell laptop -- which means that I do not have media (DVDs or USBs) for installing Windows and drivers; instead, the installation files are on my "recovery partition". (My recovery partition is still there -- I didn't touch it when I installed ubuntu.)
Is it still possible to reinstall Windows without messing up ubuntu? If so, how do I start?