Let's do a run down of the necessary software mentioned earlier.
Microsoft Visual C# can be downloaded free if you get the express edition. You can download it at http://www.microsoft.com/express/downloads/
You can also download the entire Visual Studio including visual basic and visual c++ as an ISO image (these can be tricky, see below for details on reading ISO images). Even on a blazing fast computer, downloading visual studio will take two hours at most, though.
WARNING: make sure that you get the 2008 edition and not 2010. This may seem backwards, but the Cosmos user kit has yet to support 2010.
The cosmos user kit is the platform that we will write our OS in. It's an all-in-one micro-kernel operating system that is written in 100% C#. You can download it at http://cosmos.codeplex.com/releases/view/35194
A note about ISO images:
If you opted to download the entire visual studio, then you're going to need to read the ISO image file. An ISO image is a map of a virtual DVD, using the same encoding as any other disk. You have two option: Use a program like nero or roxio to burn the image to a CD-ROM then insert that disk into your computer and download it (The latest Windows XP comes with Roxio, and Windows 7 comes with Nero pre-installed. Other than that, you will almost certainly find something on your computer that will burn a CD. Explore a bit), or you can use Daemon tools lite edition to read the file directly.
Daemon tools lite is free and can be found at http://www.daemon-tools.cc/eng/downloads
A: After downloading it, running the setup program, and re-booting, fire up Daemon tools and click Add File (the picture of the CD with a plus sign).
B: Find the image, and open it.
C: Now, select the file and click Mount. A popup (see pic') will show you some options, click "run setup.hta". This will install Visual Studio. Alternatively, you can find setup.hta in the virtual drive that was created, located in My Computer under Devices with removable storage.