You forgot to select the bootloader's initial install disk, this is easily fixed however.
1) Boot into ubuntu and type the following:
sudo grub-install /dev/sdb Note: Ensure the the thumbdrive is indeed
/dev/sdb through disk manager in Ubuntu. This will put the bootloader pointer for the BIOS onto the thumbdrive.
sudo update-grub will update grub's list of OS' just to be sure.
2) Reboot into grub. You should be presented with an aubergine menu with entries that looks like
Ubuntu 12.04, with linux x.x.x
Ubuntu 12.04, with linux x.x.x, recovery
Memtestx86, serial output xx
Windows 7 on /dev/sda1 (Loader)
Select the windows entry, while hammering F8. When a second (black, grey and white) list comes up, select repair your computer.
Just to be sure, remove the thumbdrive at this point.
Select your windows installation if prompted, and select the first option if given a list of icons with descriptions. This will restore the Windows Bootloader pointer, and allow Windows to boot. (This system assumes windows can't boot and checks things to make sure it can.