No option to install alongside Windows 7
Solution 1:
I think that you already have 4 primary partitions for Windows 7 (Ubuntu cannot create its partitions because you cannot create more than 4 primary partitions) and so Ubuntu can't show you automatically to install along Windows 7. You have to create manually the space for Ubuntu with GParted and then restart the installation of Ubuntu. Here is a guide on the dual booting Ubuntu-Windows:
http://ubuntuguide.org/wiki/Ubuntu:All#Dual-Booting_Windows_and_Ubuntu
If you are unsure when you are partitioning, ecc., please ask a new question here.