My Laptop is installed with Ubuntu 12. Now I want to install Windows 7 along with. Is it possible to keep Ubuntu and Windows in one partition? As in my Laptop computer there in only one partition of 500GB.
No, You can't install Windows and Ubuntu in the same partition.
But, I guess, You are referring to the disk by mentioning partition. Yes, You can install Windows and Ubuntu in the same disk by creating separate partition for each OS. In simple word, A partition is a logical division of the whole Disk, so that, You can feel, you have more disk.
Look at these question for getting help in installing Windows after installing Ubuntu:
You can have both, Windows and Ubuntu on a single partition by installing Ubuntu insidde Windows using Wubi. This means that you will have to repartition your drive to install Windows on this partition first and then install Ubuntu with Wubi on this partition. There is no way to install Windows within Ubuntu other than running Windows in a virtual machine.
In case you choose to not install Windows in a virtual machine I would recommend you backup your Ubuntu, repartition your drive for a separate Ubuntu, and a Windows partition, and do a fresh install of both operating systems as dual boot.