Fandt selv ud af det, hvorfor skal microsoft gøre det hele så svært?
http://social.msdn.microsoft.com/forums/en-US/sqlexpress/thread/2d46d74d-ea50-4d1f-bbcf-fedb2b012566/"I had the same problem but managed to get around it.
SQL Server Express 2008 removes the installation media after you finish installing it.
I needed to add some more features to an existing installation.
Follow my instructions below and i think you will find success.
1. Use the original SQL Express 2008 .exe file, click on it as you would normally do to instal it
2. You will prob now get the standard windows "open file - security warning" click run
3. it the begins to extract the files, make a note of what directory it is extracting to. This directory is a temporary folder and by default it will be C:\ followed by a folder name which will a random set of letters and numbers "hjlj12w123j12lj123k" for example.
4. Once setup has finished and the SQL Server Installation Center window pops up, copy that folder from C:\hjlj12w123j12lj123k to your deskop and close the SQL Server Installation Center.
5. Now open SQL Server Installation Center that is already on your computer. Start - Microsoft SQL Server 2008\ Configuration tools\SQL Server Installation Center
6. click on the installation tab and install as you were doing before. when prompted for the installation media, point it to the "hjlj12w123j12lj123k" folder no on your desktop.
that should work. either delete the "hjlj12w123j12lj123k" fodler afterwards or rename it and store it some where sensible."