system installation - Dual boot Ubuntu and Windows?

I tried to install Ubuntu alongside my windows 7.But the Ubuntu installation still doesn't detect windows on the system. It gives me the options to erase all data on the hard drive or do something else, and if I do something else then I get a list of partitions.

“Install alongside” option missing.
What else can I do to get the installation to detect windows?

Thanks for any help :) !