Dual booting requires nothing special except a basic knowledge of how partitioning works and what to do during the setup process.
For example, let's use the figure 500gb. That's the size hard drive you're playing with here in the following example. Say you primarily want to use Windows, well, you'd go about partitioning Windows so the majority is set for that. I'm the opposite. I use Ubuntu for everything, and Vista for gaming. Since Vista is pretty huge, and Battlefield and GTA4 isn't exactly 1gb in size, I gave Vista 80gb in size, with Ubuntu taking up the remainder (about 420gb).
You always want to install Windows first. The reality is, the Windows boot loader hates everybody, while Grub (Linux's boot loader) can tolerate it. More or less, install Windows first, then Linux second. When you do it in this order, Grub kicks Window's boot loader to the curb and Grub takes over. If you do this in a reverse order, the Windows boot loader does the same thing (kicks Grub out) however the Windows boot loader does not pick up Linux, which defies the point of what you're trying to do.
Easiest way to do this is instead of hitting next next next next in the partitioning menu when you go to install Windows, erase all partitions that are present on the hard drive (assuming you want to start FRESH with ZERO data on the drive) and select a partition the size accordingly to what you want Windows to use. If you want to give Windows 400gb of the 500gb drive, do that. There's no right/wrong answer here. If you want to use Linux for "experimental" purposes, then you can reserve at a minimum (that I recommend) of about 15-20gb.
The important thing is, if you want to make it easy on yourself, Windows first, Linux second. Of course you can do this the other way around, but it requires setting up the boot loader afterwards. Example - if you install Linux, THEN Windows, you have to recover Grub to get both to be recognized. I believe there's instructions on Ubuntu's web site regarding this if you ever run into this.
If you do this, when you boot up it'll have a grub menu asking you which OS you want to boot to - Ubuntu or Windows. Then you can boot accordingly.