Hi Santosh,
There is a lot of difference in windows form and WPF designer. WPF designer is entirely XAML based. The amount of rework will completely depend on you application. However you can check out this link for Windows form conversion to WPF tool.
http://wf2wpf.codeplex.com/SourceControl/list/changesetsAlso you can refer this forum for more details on Windows form to WPF conversion.
http://social.msdn.microsoft.com/Forums/en-SG/csharpgeneral/thread/a024e9da-d015-4b76-805b-0ec7a1c57b3aHope this resolves your query.
Please let me know if you have any other queries
Regards,
Padmaja