As I'm sure you've discovered, Ubuntu has tools to install on the same hard drive as another OS such as Windows, by creating a partition on that same drive (though this normally works fine, this is definitely not recommended as there is always a risk you will overwrite essential parts of your existing OS).
If you have actually partitioned your drive and then Ubuntu has been installed on the partition as Win7, then it is likely that partition was wiped and Win7 will no longer be accessible as Ubuntu has replaced it on that partition.
When you use the option to install Ubuntu on the same drive as another OS, what is meant to happen is that it installs the GRUB loader and alters some code in the MBR (Master Boot Record), this enables Ubuntu to be loaded totally independent of Windows.
Therefore if this process completely correctly then both OS are still installed on the same HDD, when you boot your computer, you should get a screen giving the option which OS to boot. Just choose Windows 7.
If this isn't the case, you might want to start thinking about getting your Windows Recovery Disk, that or reformat your HDD and reinstall Windows 7 with a properly, assuming you have it on disc.