I just need to know if I need the same framework to develop an app for Windows 8 for Tablets (Windows RT) and PCs or the tablet one still uses .NET compact framework.
The only type of applications that run on Windows RT (ie. the Tablet/ARM version of Windows 8) are Windows Store Apps. These are full-screen applications that run on top of the WinRT API.
You can use a subset of .NET 4.5 on these devices, and use XAML to build your interface just like you would with WPF on the desktop.
You can read more on MSDN - .NET for Windows Store apps overview. This article describes a lot of the changes between the main version of .NET and the Windows RT subset that's available to you. Generally, Windows.Runtime will provide alternatives to some of the .NET methods that no longer exist.