Unless they changed this dramatically since VS2k8, you'll see that when you create a new test project, you'll get a new "solution folder" in your solution called "Solution Items" with a .testRunConfiguration
file in it which contains the settings.
If not, then you can create the "solution folder" yourself. Right-mouse click on your solution and select Add -> New Solution Folder. Right-mouse click on the folder and select Add -> New Item. Select "Test Run Configuration" under "Categories". If you click on the project, you will not see these choices.
If that doesn't still work in VS2k10, I'll be interested in knowing.
Response to JustLoren's Comment I did a quick Google search and found this: http://social.msdn.microsoft.com/Forums/en/vststest/thread/8ef10a3a-d4d5-4931-9054-df1d81ee4842..
Apparently, they did change the file extension from .testrunconfig to .testsettings in VS2k10. I believe that the key to solving your problem is likely to properly create the Solution Items
solution folder and add your configuration file there.