(http://www.blogcdn.com/www.downloadsquad.com/media/2009/11/vhd-attach-adfgae546.jpg)
While Windows 7 can manage VHDs like physical disks, mounting and dismounting them is a bit overcomplicated. You've got to open the disk management snap-in, click attack, then browse for your VHD. VHDAttach makes the process as simple as it can get: open the folder where your VHD is located, right-click it, and choose attach (or detach) from the context menu.
http://www.jmedved.com/default.aspx?page=vhdattach&rendering=xhtml