@Berengar: I suspect that you do not have the Parallels Tools installed. Parallels Tools are installed in the guest OS and provide support for copy & paste, drag & drop, and Retina resolution in Win7 and Win 8 guests.
To install the Parallels Tools, bring your guest OS window into focus, and then choose "Install Parallels Tools" from the Virtual Machine menu in the Mac menu bar.
I was using a 15" Retina MacBook Pro. Here are some of the specs:
2.7 GHz Intel i7 with 16GB of RAM
Nvidia GeForce GT 650M with 1GB RAM (standard on the Retina)
This is one really great Mac, but you won't need this much horsepower to effectively use Visual Studio on a Mac.
Of all these specs, the most important is RAM. Depending on the size of your VS project, you might need to give Win 8 a gig or two (or more) of RAM, and you, of course, don't want the Mac OS starved for RAM, so an 8GB Mac is the smallest I would recommend. A fast processor is always great, as is a fast disk, but an SSD is not required.