xWinForms 1.3 has been release on GameProjects.com.
This new version includes a library DLL which you can use instead of adding the source to your project. It can be found in xWinFormsLib.

1.3 Updates :

xWinFormsLib.DLL created from xWinForms v1.3
Added Menu/Submenu mnemonics (key shortcuts)
Added Menu/Submenu keyboard control (alt, arrows, enter and escape)
Added Textbox multiline support (not editable, fixed line width)
Added TAB/Shift-TAB input to set focus on the next/previous control
Added CTRL-TAB input to set focus on the next form
Fixed Progressbar to use it's full length
Fixed Submenus (OnMouseOver open submenu)
Fixed Textbox input keys (added every symbols)

Known remaining bugs :
Slider doesn't slide yet.
Cannot load more than 2 layers of submenus from xml files.
User does not see which control is focused.
Textbox timer/cursor issue when the text is too long.
Minimized form positioning issue when more than 3 are minimized.
TextButton not merged with Button class yet.

Hopefully I will resolve all the remaining bugs in v1.4 and be able to focus my energy on other projects.