I had to do a similar thing. I needed to make Windows the only OS on a hard drive without formatting the drive/reinstalling. What I did was:
Boot into windows run BootRec.exe /fixmbr . This will get Windows7 to fix the Master Boot Record (MBR). Since it doesn't recognize Ubuntu this will set it so Windows7 is the only boot option.
Then you can boot into an Ubuntu CD. Use Gparted to remove the Ubuntu (Ext4) and Swap partitions. Then, expand the Windows Partition to fill the Hard drive.
Please be careful with each step as a mistake could wipe the wrong info. Also, make sure (and make sure again) that you have all the data you need off of the partitions you're removing.