So. First of all, Wubi is about trying out Linux, not about totally using it (you will have some speed decrease, problems can occur, bla bla. I would NOT recommend using that "install it in Windows" at all).
About the partition. You can do it from the "Computer management" in Windows, or using Acronis Disk Director suite. (I don't really trust Ubuntu's manager since it ruined my partition table , so I just stick to Win/acronis).
That's all I guess. If you want a permanent installation, consider using the Manual method. (That means at the install of Ubuntu, select the manual partitioning. You need basically 3 partition for using it long term.
You need a
/ , a
/home and a
swap . Not sure how familiar you are with this.
/ Contains the system files, like applications and such (usually I create a 15gb partition for that, but many people is fine with 10gb..).
/home will keep your personal files (music, Documents, YOUR SETTINGS!. Making a separate partition just for this will help you at the next reinstall. You can just 'assign' the partition as /home, and you dont have to format it. If you are lucky, even your settings will be back 1:1).
Swap is a partition without normal fs type, its just for swap. Like paging file in Windows, but here its a different partition (its needed for hibernation, when you run out of RAM. There is a saying that you need twice as much as you ram you have (so I have 2048mb ram, I would have to create a 4096 mb swap). But that's just a dumb saying. You are fine with at least as big as your ram partition (so about ~2100mb, ~4100, and so on. Bigger than your ram because if you hibernate, it have to save the running stuff.))