Having tried a few Alt-Tab windows switcher, I want to write one to suit my own needs. Are you aware of any open source Alt-Tab windows switchers? If it already exists, I don't want to start from scratch :)
If it's source code you're after you may look at TaskSwitchXP sources: http://www.ntwind.com/software/taskswitchxp/download.html
The same company offers VistaSwitcher, however that one is not open source.