I misread a part of your original post and became more clear now.
You could use DATEADD(wk, DATEDIFF(wk,0,Date), 0) to get the first day of the week and be able to group them.
Luis C.
General Disclaimer:
Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?
How to post data/code on a forum to get the best help: Option 1 / Option 2