It's been a long time since I've done it on my own system, so bear with me. Back up your system first! Also, I'm not super tech-savvy, so if anyone else has suggestions for improvements, go ahead and jump in. I know that I didn't do it in the most optimal way when I partitioned everything...
First, read this: https://help.ubuntu.com/community/DiskSpace
The way that I set up my drive, I wanted a shared partition between Windows and Ubuntu for storing all of my files so that I can access them from either partition.
If you want to set it up with the shared partition, I would suggest moving all your files into external storage for now, so that you can shrink down your Windows partition. (I didn't do this and now my Windows partition is much too large-- I'm going to have to do some juggling to reallocate space...).
I used the Wubi ISO burned to a disc to run the installation. You'll need to change the boot options so that your computer boots from the disc, since you'll use the gParted tool to do the re-partitioning.
In order to have more than 4 primary partitions, you'll need an extended partition. Figure out how much space you want to give to Windows-- if I'd been smart and moved all my files, I would've given it about 75Gb. But that's entirely up to you. I've heard people give it as little as 30Gb, but I don't know how well the system runs with a partition that small... The recovery partition is 4Gb. Everything else will be allocated to Ubuntu.
**Note: I have a 300Gb hard drive on a Windows 7 64-bit system.
/dev/sda1 is the Windows partition. /dev/sda2 is the recovery partition. Shrink down sda1 to the size that you want.
Create an extended partition, /dev/sda3. The first partition within the extended partition will be your swap partition-- I gave it about 10Gb. Next is root, which is ext4 format; I gave it 15Gb. I put the shared partition (ntfs format) next; the path for this one was /mnt/Shared (the size of this one will depend on how much space you allocate to everything else). The last partition is the Ubuntu partition, /home-- I think I gave this one too much space as well (50Gb?)
This article has great information, and I wish I'd read it before I did my own system. I suggest you read it as well: