My work is like making interface with visual studio, like preparing GUI for rs 232.
For that i have to purchase Microsoft Visual Studio.
can anyone tell me which version is suitable for me to purchase ?

Depends on what you mean by GUI. If you mean MFC then you just buy the Professional version. If you are not going to use MFC then you might be able to get along with the free Express version and download some free libraries that let you write gui programs, such as wxWidgets. There are also Express editions of c++/CLR (Windows Forms), C# and VB.NET.

Before spending hundreds or thousands of dollars for something you don't need check out the free versions to see if they do what you want.