蛋疼的VS2010 tab group

http://superuser.com/questions/232031/why-does-my-visual-studio-2010-default-to-a-horizontal-windows-split-if-i-quit-t 

1. double click .sln file --->  horizontal windows split

2. open VS2010-->file-->open project/solution-->.sln file--->vertically windows split.

just use  the second one!