I\'ve made a WPF Browser Application that hosts old WinForms controls (I haven\'t migrated fully to WPF yet). Using WindowsFormsHost means my Browser App requires Full Trust
It will be possible in .Net 4.0 planning to be released in the first half of 2010. It is now in a beta phase, but it comes with a go live license which allows you to 'go live' even with a beta version of the .Net framework.