Tombstone, tombstoning.  It is somewhat difficult to get tombstoning right, and this article is a long one at 7 pages, but you NEED to read it.

http://create.msdn.com/en-US/education/catalog/article/tombstoning_wp7_games

It is a Word file, if you don’t have Word on your system, then get the Word Reader/Viewer at:

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=4

Or you can upload the document to Skydrive and use Office Live!

By the way, if you have Office Starter on your system, great!  Office Starter has some hidden value that you should check into!  Office Starter is not a trail version, and you can keep using as long as you need to.  It is only available on new PCs though.