I want to dual boot ubuntu 12.10 with Windows 7 on my laptop. I checked some online guides but each one does it differently. Some only create a / (root) partition and a swap partition while others create a / (root) partition, a boot partition, a home partition and a swap partition. Which guide should I follow? Please help. And what size should I give every partition considering I am going to install Ubuntu on 200GB of my 500GB hard drive?
This depends a bit on how serious you're considering to be with Ubuntu, but in general your answer can be summarized as much:
Going deeper in, unless you have very specific needs, you will not need any other mounting points to partitions other than the three above.
However, as you'll be dualbooting with Windows you have to ask yourself whether or not you'll be seriously using Ubuntu. If you'll be using it every now and then, I recommend you just use your already existing data partition for Windows.
On the other hand, if you end up staying here... it'll be a good idea to have a proper "/home" - rather than just mounting your Windows-partition(s).
I'd recommend having at least 4 primary partitions for a dual-booting computer: 1st for windows OS; 2nd for the Ubuntu file system (plus a logical partition to serve as a swap); a 3rd as a shared Data partition in NTFS to serve both operating systems -- vital for both security of data and to not have redundancies with my programs that sync massive amounts of data locally (Zotero, Dropbox, etc); and 4th as a /home/ folder for Ubuntu.
However, you may have discovered that Windows takes more than one primary partition (it gobbled up 3 in my case, and I was able to reduce it to just 2), which means you may have to set up /home/ partition as a logical partition under the Ubuntu partition. When doing future re-installations of Ubuntu, just make sure to not erase the logical partition for home, and remember to mount it as /home. This can be done during the 'do something else' stage of installing Ubuntu when you specify under which partitions to install Ubuntu and mount-points.