I think W7 is very safe, if you :
- don’t use Internet Explorer.
- don’t install Java.
- don’t use email client program and use something like Gmail. (don’t download local copies of e-mails)
- use Firefox and block ads, popups, and redirection
- check where the links are taking you in status bar before clicking every time.
- don’t open attachments from guys you don’t know.
- don’t download and install free software that would install some “extras”. (You can google and see if the installer may do something weird before downloading.)
- read up on what’s updated in monthly windows updates, and install as necessary.
- use legit software.
- use page previews for Google search results before actually clicking on the links.
I have been using my W7 x64 PC just like I used to use my Macs in the past, and I really don’t see any reason to fear internet. I use 64bit Firefox Nightly as well - nobody would bother to exploit something with such a small user base. 
I do have MS Security Essentials on my machine just in case, but I think Firefox and Gmail pretty much blocks anything bad from happening.
My DAW is connected 24/7. DPC latency @ idle hovers around 15-20 micro seconds on my machine. I’ve thought about dual booting my machine before I assembled it, but I really don’t see the need after 2 years of constant use.
If you really think it’s necessary, you might as well go Linux for the general use partition. W7 & W8 are said to be more secure than OS X, though, and I seriously doubt that you need to worry about viruses like on XP.