To install Kikuyu, go to http://kikuyu.ruisu.net/publish.htm. That is always where the newest version of the beta will be. When a new version is published Kikuyu will ask you if you would like to update. You can check the version your using by clicking Help → About.

System Requirements
Kikuyu requires Windows NT 5.1 or greater.
Kikuyu also requires the .NET Framework 3.5 and Windows Installer 3.1. Those two items also require Windows NT 5.1 or greater. If you don't know if you have either of these, just go to the download page and click install. If you have Vista you already have these. If you don't have Vista you likely have the .NET Framework and Windows Installer already, but may need a small update on your .NET version. In any case, this will all be handled by clicking install.
It runs in native 32 or 64-bit mode, depending on your OS.

Here is a list of Windows NT versions:

Can Kikuyu run on Mono?
No, I'm afraid I've gone and made a .NET 3.5 program. I believe Mono only supports up to version 2.0.

If Kikuyu is not a WPF application, then why does it run on .NET 3.x
The way  Kikuyu started, it was only intended for my personal use. I used the default settings in Visual Studio. Even though it's not a WPF application, I wound up using some classes that aren't in version 2. So, I can't simply switch the runtime during compilation. I'd have to look in to how to do these things that .NET 3 might handle in a simple function. But around 96% of Windows PCs run NT 5.1 or greater, so I don't know how worth it this will be. I may eventually look in to converting Kikuyu to run on the .NET 2.0 Framwork, which will let it run on older versions of Windows and Mono. Either that or look at making Kikuyu a WPF application.