Just wanted to share this solution as I've seen a number of people having issues with Mountain Lion and Time Machine to WHS 2011. All the credit of course goes to the website below. Also, Mountain Lion wouldn't let me create the disk image directly to the share folder, from what I've read this is by design. Instead, I created the image to an external hard drive I had laying around and then dragged the sparse bundle over to the folder I created on my server. Then followed the directions and Time Machine is working fine, backing up to my server. Hope this helps.
http://basilsalad.com/how-to/create-time-machine-backup-network-drive-lion/