Did you get this message "The install in progress conflicts with a previously installed Microsoft Office 2010 Server product" after an uninstall (on e.g. your development server) then it's very likely that there are som Office Web Apps garbage in your registry.
You may start with this article: "Installing Sharepoint 2010 over a previous version", or (as I did) just open regedit, search for "Web Apps" and just delete every entry you can find. Easy as hell, but proobably not something you would do on a production server :-)
What web parts comes with which SharePoint (Foundation, Standard and Enterprise) version / SKU / License?
I'm happy to say that I didn't have to compile this list myself, but can safely redirect you to Ari Bakker's blog, and his nice page: SharePoint 2010 Web Parts by License Type.
Sumarized these are the important ones that comes for free (SharePoint Foundation):
- Image Viewer
- Page Viewer
- Picture Library Slideshow
- Simple Form
- User Docs
- User Tasks
- Xml Viewer