It was already possible for students and teachers to obtain a free version of Visual Studio 2010 Professional but now this Microsoft offer has been extended to a number of other groups. One group being any individual who is thinking about becoming a web developer.
The extended Microsoft offer provides immediate download and 3 year license for a huge range of products such as Visual Studio 2010 Professional. This appears to open the door to Visual Studio to just about everyone in the arduino community.
To take advantage of the offer you will need to sign up for the free Microsoft WebSiteSpark program. Once you have signed up you will see a big button allowing you sign up for downloads. The big button actually signs you up to the microsoft developer network (msdn).
On msdn you will see a large list of available downloads on your msdn downloads page. Choose a Visual Studio 2010 Professional download from the list and install it.
If possible, use the Web Download option because it is simpler. Otherwise, to the right of each "download link" is a link that will show your personal license key for the selected product (keep it private).
Stumbled across this while looking at Arduino stuff. Just got myself a key now