I would suggest getting DM 4.6. 4.7 was designed and released with the blackberry storm in mind. Still has a few bugs with the curve.. It works for some curves but still has a lot of problems. 4.6 is the most solid for curves.
I agree with Tae and Trem, 4.7 is made for the storm and i have heard it has issues when run with a Curve. I would jump down to 4.5 or 4.6, i did my update last night with 4.5DM and it worked flawlessly. As for updating with windows 7 you should be perfectly fine to do so.