I want to develop a feature(-event receiver) to override default.aspx. I want to use a webpart-page instead and add some webparts. I don't know how to override it. I know how to build a new webpart-page, but I don't know how to find default.aspx and replace it.Could you please provide me the information I'm missing?
Have a look at these article, it also summarizes some of the most common approaches to have web part deployed on existing page or with a new page http://blogs.msdn.com/b/uksharepoint/archive/2011/04/04/provisioning-web-parts-to-a-page.aspx
Also using the AllUsersWebPart is the prefered approach for Page Layouts in Publishing site, also known as declarative (versus writing code in a feature receiver to inject it into a page) - see here for more http://dotnetmafia.sys-con.com/node/1046923/mobile
Waldek goes into more details if you prefer still the programatic approach http://blog.mastykarz.nl/provisioning-web-part-instances-in-a-structured-and-repeatable-way/ or to insert it direclty in a an existing RTE zone http://blog.mastykarz.nl/programmatically-adding-web-parts-rich-content-sharepoint-2010/