OpenLaszlo currently generates script source that is compatible with ECMAScript Release 3 which is then compiled into SWF6 through SWF8 ActionScript. Legals adds additional compile support for SWF 9 and DHTML. The initial release supports Javscript 1.4/Jscript 5.6, Firefox 1.5 and IE 6. Future releases will support Javascript 1.5. The Legals page also has a link to a picture explorer sample application that has been compiled to both Flash and DHTML. Carlos Perez blogged last week that the DHTML support was reportedly based on the dojo toolkit.
According to the project plan, they are also considering compilation targets to XAML/Windows Presentation Foundation, but that would be in the distant future. Read/Write web has a great article summarizing the current status of OpenLaszlo, Adobe Flex, and Windows Presentation Foundation, all of which take a form of XML dialect and convert them into browser-based rich internet apps.