When you open a solution in Visual Studio 2008 (or ealier versions for that matter), it opens all the documents that you did not close before you closed Visual Studio. Is there
I dont think there is an option for this (or I couldnt find one) but you could probably write a macro to do this for you on project open.
This link has some code to close open files which you could adapt: http://blogs.msdn.com/djpark/
I couldnt find the answer to this particular question but a good link for ide tips and tricks is: http://blogs.msdn.com/saraford/default.aspx